Method of using fibrous tissue sealant

ABSTRACT

Disclosed herein is a fibrous tissue sealant in the form of an anhydrous fibrous sheet comprising a first component which is a fibrous polymer containing electrophilic or nucleophilic groups and a second component capable of crosslinking the first component when the sheet is exposed to an aqueous medium, thereby forming a crosslinked hydrogel that is adhesive to biological tissue. The fibrous tissue sealant may be useful as a general tissue adhesive for medical and veterinary applications such as wound closure, supplementing or replacing sutures or staples in internal surgical procedures, tissue repair, and to prevent post-surgical adhesions. The fibrous tissue sealant may be particularly suitable for use as a hemostatic sealant to stanch bleeding from surgical or traumatic wounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/968,503, filed Aug. 16, 2013, which is a Continuation of U.S. patentapplication Ser. No. 13/129,658, filed May 17, 2011, issued as U.S. Pat.No. 8,545,871, which is incorporated herein by reference and which is aU.S. National Stage Application filed under 35 U.S.C. Section 371 ofPCT/US2009/055487, filed Aug. 31, 2009, which claims priority of U.S.Provisional Application Ser. No. 61/115,968, filed Nov. 19, 2008.

FIELD OF THE INVENTION

The invention relates to the field of medical adhesives. Morespecifically, the invention relates to a fibrous tissue sealant in theform of an anhydrous fibrous sheet comprising two or more crosslinkablecomponents that react to form a crosslinked hydrogel that is adhesive tobiological tissue when the sheet is exposed to an aqueous medium.

BACKGROUND OF THE INVENTION

Tissue adhesives have many potential medical applications, includingwound closure, supplementing or replacing sutures or staples in internalsurgical procedures, adhesion of synthetic onlays or inlays to thecornea, drug delivery devices, anti-adhesion barriers to preventpost-surgical adhesions, and as a hemostatic sealant. Conventionaltissue adhesives are generally not suitable for a wide range of adhesiveapplications. For example, cyanoacrylate-based adhesives have been usedfor topical wound closure, but the release of toxic degradation productslimits their use for internal applications. Fibrin-based adhesives areslow curing, have poor mechanical strength, and pose a risk of viralinfection. Additionally, the fibrin-based adhesives do not bondcovalently to the underlying tissue.

Several types of hydrogel tissue adhesives have been developed whichhave improved adhesive and cohesive properties and are nontoxic. Thesehydrogels are generally formed by reacting a component havingnucleophilic groups with a component having electrophilic groups, whichare capable of reacting with the nucleophilic groups of the firstcomponent to form a crosslinked network via covalent bonding. However,these hydrogels typically swell or dissolve away too quickly, or lacksufficient adhesion or mechanical strength, thereby decreasing theireffectiveness as surgical adhesives.

Kodokian et al. (copending and commonly owned U.S. Patent ApplicationPublication No. 2006/0078536) describe hydrogel tissue adhesives formedby reacting an oxidized polysaccharide with a water-dispersible,multi-arm polyether amine. These adhesives provide improved adhesion andcohesion properties, crosslink readily at body temperature, maintaindimensional stability initially, do not degrade rapidly, and arenontoxic to cells and non-inflammatory to tissue.

It is known that hydrogel tissue adhesives may be formed by mixing twoaqueous solutions, each of which contains one of the crosslinkablecomponents. The two solutions can be premixed using a mixing devicebefore application to the desired site or can be applied separately andallowed to mix at the site of application. Additionally, the use ofdried hydrogels and dried hydrogel precursors has been described (seefor example, Rhee et al. U.S. Pat. No. 5,874,500, Sawhney et al., U.S.Pat. No. 6,703,047, and Odermatt et al., U.S. Patent ApplicationPublication No. 2006/0134185). However, for some applications, forexample a hemostatic sealant, it may be advantageous to have the tissueadhesive in a fibrous form which would be more effective in absorbingblood to help control bleeding and thereby having an easier application.

SUMMARY OF THE INVENTION

An anhydrous fibrous sheet comprising a first component of fibrouspolymer, said polymer containing electrophilic groups or nucleophilicgroups, and a second component capable of crosslinking the firstcomponent when said sheet is exposed to an aqueous medium in contactwith biological tissue to form a crosslinked hydrogel that is adhesiveto the biological tissue; wherein the second component is a fibrouspolymer having a backbone structure the same as or different from thefibrous polymer of the first component and containing electrophilicgroups if the first component contains nucleophilic groups or containingnucleophilic groups if the first component contains electrophilicgroups; or the second component is a coating on the fibrous polymer ofthe first component, wherein said coating contains electrophilic groupsif the first component contains nucleophilic groups or nucleophilicgroups if the first component contains electrophilic groups; or thesecond component is a dry powder dispersed and entrapped withininterstices of the fibrous polymer of the first component, wherein saidpowder contains electrophilic groups if the first component containsnucleophilic groups or nucleophilic groups if the first componentcontains electrophilic groups is provided.

Also provided is a method for preparing a crosslinked hydrogel usefulfor applying a fibrous coating to an anatomical site on tissue of aliving organism, the method comprising the steps of a) applying to ananatomical site an anhydrous fibrous sheet of the invention and b)contacting the first component and the second component of the anhydrousfibrous sheet with an aqueous medium and allowing the first componentand the second component to crosslink on the anatomical site to form ahydrogel that is adhesive to the tissue of the anatomical site.

Further provided is a method to obtain an adhesive hydrogel useful tostanch bleeding from a surgical or traumatic wound in tissue of a livingorganism, the method comprising the steps of a) applying to the wound ananhydrous fibrous sheet of the invention and b) allowing the sheet tohydrate by absorbing blood, whereby the first component and the secondcomponent crosslink to form a hydrogel that is adhesive to the tissue.

Additionally provided is a method for obtaining an adhesive hydrogeluseful for applying a coating to an anatomical site on tissue of aliving organism, the method comprising the steps of a) applying to thesite the first component of an anhydrous fibrous sheet of the invention,b) applying to the site an aqueous solution or dispersion comprising thesecond component of an anhydrous fibrous sheet of the invention; and c)allowing the first component and the second component to crosslink onthe site, to form a hydrogel that is adhesive to the tissue.

Also provided is a method for applying a coating to an anatomical siteon tissue of a living organism comprising the steps of applying to thesite a first component of fibrous polymer containing electrophilic ornucleophilic groups; applying to the site an aqueous solution ordispersion comprising a second component capable of crosslinking thefirst component, wherein the second component contains electrophilicgroups if the first component contains nucleophilic groups or containsnucleophilic groups if the first component contains electrophilicgroups; and allowing the first and the second component to crosslink onthe site to form a hydrogel that is adhesive to the tissue.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a scanning electron micrograph (SEM) of the dextranaldehyde/dextran fibrous polymer described in Example 1.

FIG. 2 is a scanning electron micrograph of the poly(vinylalcohol-co-vinyl amine) fibrous polymer described in Example 10.

DETAILED DESCRIPTION

As used above and throughout the description of the invention, thefollowing terms, unless otherwise indicated, shall be defined asfollows:

The term “anhydrous fibrous sheet”, as used herein, refers to a nonwovenfiber in the form of a sheet or mat which is substantially water free.

The term “fibrous polymer”, as used herein, refers to a natural,synthetic, or semi-synthetic polymer which is in the form of a fiberhaving an aspect ratio (ratio of length to diameter) of at least 1,000.

The term “crosslink” refers to a bond or chain of atoms attached betweenand linking two different polymer chains.

The term “crosslink density” is herein defined as the reciprocal of theaverage number of chain atoms between crosslink connection sites.

The term “oxidized polysaccharide” refers to a polysaccharide which hasbeen reacted with an oxidizing agent to introduce aldehyde groups intothe molecule.

The terms “equivalent weight per acetoacetate group”, “equivalent weightper amine group”, and “equivalent weight per aldehyde group” refer tothe molecular weight of the compound divided by the number ofacetoacetate, amine or aldehyde groups, respectively, in the molecule.

The term “water-dispersible polymer having nucleophilic groups” refersto a natural, synthetic, or semi-synthetic polymer containing a number“n” of nucleophilic groups (i.e., electron donating groups), such asprimary amine groups, and which is water soluble or able to be dispersedin water to form a colloidal suspension capable of reacting with asecond reactant containing a number “m” of electrophilic groups in anaqueous solution or dispersion to form a crosslinked hydrogel, where mplus n is greater than or equal to 5. In certain cases, a givenfunctional group may have the properties of either electrophilicity ornucleophilicity depending upon the reaction conditions. Therefore,additionally as defined herein, water-dispersible polymers havingelectrophilic groups include natural, synthetic, or semi-syntheticpolymers containing “m” acetoacetate groups which when treated withaqueous base to form the nucleophilic conjugate base of acetoacetate arecapable of reacting with electrophilic groups, such as aldehydes.

The term “water-dispersible polymer having electrophilic groups” refersto a natural, synthetic, or semi-synthetic polymer containing a number“m” of electrophilic groups (i.e., electron accepting groups) such asaldehyde, acetoacetate, N-hydroxysuccinimidyl ester, or isocyanate, andwhich is water soluble or able to be dispersed in water to form acolloidal suspension capable of reacting with a second reactantcontaining “n” nucleophilic groups in an aqueous solution or dispersionto form a crosslinked hydrogel, where n plus m is greater than or equalto 5. Additionally as defined herein, water-dispersible polymers havingelectrophilic groups include natural, synthetic, or semi-syntheticpolymers containing “m” carboxylic acid groups which can be activated,for example using a water-soluble carbodiimide, to react withnucleophilic groups. It can be appreciated by one skilled in the art,that not all possible nucleophiles will form a usefully stable crosslinkin combination with all possible electrophiles. For instance, it is wellknown that a thiol will not form a particularly stable bond with analdehyde or an acetoacetate under the conditions of hydrogel formationdetailed herein. However, a thiol will form a reasonably stablethioester bond upon reaction with an N-hydroxysuccinimidyl ester underthese conditions.

The term “semi-synthetic polymer” refers to a naturally occurringpolymer that has been chemically modified, as for example to introducereactive groups into the molecule.

The term “water-dispersible polymer” refers to a natural, synthetic, orsemi-synthetic polymer which is water soluble or able to be dispersed inwater to form a colloidal dispersion capable of reacting with a secondreactant in aqueous solution or dispersion.

The term “water-dispersible, multi-arm polyether amine” refers to abranched polyether having at least three arms (i.e., branches), whereinat least three of the arms are terminated by at least one primary aminegroup, which is water soluble or able to be dispersed in water to form acolloidal dispersion capable of reacting with a second reactant inaqueous solution or dispersion.

The term “polyether” refers to a polymer having the repeat unit [—O—R]—,wherein R is a hydrocarbylene group having 2 to 5 carbon atoms. Thepolyether may also be a random or block copolymer comprising differentrepeat units which contain different R groups.

The term “hydrocarbylene group” refers to a divalent group formed byremoving two hydrogen atoms, one from each of two different carbonatoms, from a hydrocarbon.

The term “branched polyether” refers to a polyether having one or morebranch points (“arms”), including star, dendritic, comb, andhyperbranched polyethers.

The term “dendritic polyether” refers to a highly branched polyetherhaving a tree-like structure.

The term “comb polyether” refers to a polyether having a main chain withmultiple trifunctional branch points from each of which a linear armemanates.

The term “star polyether” refers to polyether having a central branchpoint, which may be a single atom or a chemical group, from which lineararms emanate.

The term “hyperbranched polyether” refers to a highly branched polyetherhaving fewer branches and less regular branching than a dendriticpolyether.

The term “% by weight”, also referred to herein as “wt %” refers to theweight percent relative to the total weight of the solution ordispersion, unless otherwise specified.

The term “anatomical site” refers to any external or internal part ofthe body of humans or animals.

The term “tissue” refers to any biological tissue, both living and dead,in humans or animals.

The term “hydrogel” refers to a water-swellable polymeric matrix,consisting of a three-dimensional network of macromolecules heldtogether by covalent or non-covalent crosslinks, that can absorb asubstantial amount of water to form an elastic gel.

The term “polyol” refers to a chemical compound having three or more OHgroups.

The term “primary amine” refers to a neutral amino group having two freehydrogens. The amino group may be bound to a primary, secondary ortertiary carbon.

The term “secondary amine” refers to a neutral amino group having onefree hydrogen. The amino group may be bound to a primary, secondary ortertiary carbon.

The term “PEG” as used herein, refers to poly(ethylene glycol).

The term “SEC” as used herein refers to size exclusion chromatography.

The term “DMAc” as used herein refers to N,N-dimethylacetamide.

The term “VAc” as used herein, refers to vinyl acetate.

The term “EW” as used herein refers to equivalent weight.

The term “MW” as used herein refers to molecular weight.

The term “M_(w)” as used herein refers to the weight-average molecularweight.

The term “M_(n)” as used herein refers to the number-average molecularweight.

The term “M_(z)” as used herein refers to the z-average molecularweight.

The term “NVF” as used herein refers to N-vinylformamide.

The term “medical application” refers to medical applications as relatedto humans and animals.

The meaning of abbreviations used is as follows: “min” means minute(s),“h” means hour(s), “sec” means second(s), “d” means day(s), “mL” meansmilliliter(s), “L” means liter(s), “μL” means microliter(s), “cm” meanscentimeter(s), “mm” means millimeter(s), “μm” means micrometer(s), “mol”means mole(s), “mmol” means millimole(s), “g” means gram(s), “mg” meansmilligram(s), “mol %” means mole percent, “Vol” means volume, “v/v”means volume per volume, “Da” means Daltons, “kDa” means kiloDaltons,the designation “10K” means that a polymer molecule possesses anumber-average molecular weight of 10 kiloDaltons, “M” means molarity,“MWCO” means molecular weight cut-off, “kPa” means kilopascals, “¹H NMR”means proton nuclear magnetic resonance spectroscopy, “ppm” means partsper million, “PBS” means phosphate-buffered saline.

The present invention provides a fibrous tissue sealant in the form ofan anhydrous fibrous sheet comprising a first component which is afibrous polymer containing electrophilic or nucleophilic groups and asecond component capable of crosslinking the first component when thesheet is exposed to an aqueous medium, thereby forming a crosslinkedhydrogel that is adhesive to biological tissue. The fibrous tissuesealant may be useful as a general tissue adhesive for medical andveterinary applications including, but not limited to, wound closure,supplementing or replacing sutures or staples in internal surgicalprocedures such as intestinal anastomosis and vascular anastomosis,tissue repair, and to prevent post-surgical adhesions. The fibroustissue sealant may be particularly suitable for use as a hemostaticsealant to stanch bleeding from surgical or traumatic wounds.

First Component

The first component is a fibrous polymer containing electrophilic groupsor nucleophilic groups. Suitable polymers are water-dispersible polymerswhich can be made into fibrous polymer form. The water-dispersiblepolymers may have electrophilic groups, such as aldehyde, acetoacetate,or succinimidyl ester; or nucleophilic groups, such as primary amine(NH₂), secondary amine (NHR), carboxyhydrazide (CONHNH₂), acetoacetate,or thiol (SH) groups. One skilled in the art will recognize that theacetoacetate group can behave as both an electrophile, when its carbonylgroups are reacted with nucleophiles, or as a nucleophile, under basicconditions in which its methylene is deprotonated to form a stabilizedcarbanion capable of reacting with electrophiles. The water-dispersiblepolymer having electrophilic groups or the water-dispersible polymerhaving nucleophilic groups may be a naturally occurring polymer, such asa polysaccharide, or protein; a synthetic polymer, such as polyvinylalcohol; a synthetic copolymer, such as poly(vinyl alcohol-co-vinylamine); or a semi-synthetic polymer (i.e., a naturally occurring polymerthat has been chemically modified), such as an oxidized polysaccharide.The synthetic polymers may be linear or branched. The water-dispersiblepolymers may be derivatized to introduce the desired reactive groupsusing methods known in the art.

Nonlimiting examples of suitable water-dispersible polymers havingelectrophilic groups include: oxidized polysaccharides having aldehydegroups, poly(vinyl alcohol) or poly(vinyl alcohol) copolymersderivatized with acetoacetate groups, and polysaccharides derivatizedwith acetoacetate groups. Nonlimiting examples of suitablewater-dispersible polymers having nucleophilic groups include:poly(vinyl alcohol) or poly(vinyl alcohol) copolymers having primaryamine groups, secondary amine groups, thiol groups, acetoacetate groups,or carboxyhydrazide groups, and polysaccharides having primary aminegroups, secondary amine groups, thiol groups, acetoacetate groups, orcarboxyhydrazide groups. Examples of these water-dispersible polymersare described below. A variety of other water-dispersible polymershaving electrophilic or nucleophilic groups are known in the art andcould be used to prepare the fibrous polymer disclosed herein, forexample see Rhee et al. in U.S. Pat. No. 5,874,500 (in particular column6, line 22 to column 9, line 6). It should be recognized that theseother water-dispersible polymers are within the scope of the invention.

Water-Dispersible Polymers Having Electrophilic Groups

(i) Oxidized Polysaccharides

Polysaccharides useful in the present invention include, but are notlimited to, dextran, starch, agar, cellulose, hydroxyethylcellulose,pullulan, inulin, and hyaluronic acid. These polysaccharides areavailable commercially from sources such as Sigma Chemical Co. (StLouis, Mo.). Suitable polysaccharides have a weight-average molecularweight from about 1,000 to about 1,000,000 Daltons, and moreparticularly from about 3,000 to about 250,000 Daltons.

The polysaccharide is oxidized to introduce aldehyde groups using anysuitable oxidizing agent, including but not limited to, periodates,hypochlorites, ozone, peroxides, hydroperoxides, persulfates, andpercarbonates. For example, the polysaccharide may be oxidized byreaction with sodium periodate as described by Mo et al. (J. Biomater.Sci. Polymer Edn. 11:341-351, 2000). The polysaccharide may be reactedwith different amounts of periodate to give polysaccharides withdifferent degrees of oxidation and therefore, different amounts ofaldehyde groups, as described in detail in the Reagent Preparationsection of the Examples below. Additionally, the oxidized polysaccharidemay be prepared using the method described by Cohen et al. (copendingand commonly owned Patent Application No. PCT/US08/05013, WO2008/133847). That method of making an oxidized polysaccharide comprisesa combination of precipitation and separation steps to purify theoxidized polysaccharide formed by oxidation of the polysaccharide withperiodate and provides an oxidized polysaccharide with very low levelsof iodine-containing species. The aldehyde content of the oxidizedpolysaccharide may be determined using methods known in the art. Forexample, the dialdehyde content of the oxidized polysaccharide may bedetermined using the method described by Hofreiter et al. (Anal Chem.27:1930-1931, 1955), as described in detail in the Reagent Preparationsection of the Examples below. In that method, the amount of alkaliconsumed per mole of dialdehyde in the oxidized polysaccharide, underspecific reaction conditions is determined by a pH titration.Additionally, the dialdehyde content of the oxidized polysaccharide maybe determined using nuclear magnetic resonance (NMR) spectroscopy. Inone embodiment, the equivalent weight per aldehyde group of the oxidizedpolysaccharide is from about 90 to about 1500 Daltons. In anotherembodiment, the oxidized polysaccharide is oxidized dextran, alsoreferred to herein as dextran aldehyde.

(ii) Poly(Vinyl Alcohol) or Poly(Vinyl Alcohol) Copolymers Derivatizedwith Acetoacetate Groups

Poly(vinyl alcohols) having different weight-average molecular weightsand varying degrees of hydrolysis are available commercially fromcompanies such as Sigma-Aldrich (St. Louis, Mo.). Poly(vinyl alcohols)suitable for use in the invention have a weight-average molecular weightof from about 20,000 Daltons to about 100,000 Daltons, more particularlyfrom about 30,000 Daltons to about 50,000 Daltons. Useful poly(vinylalcohols) have a degree of hydrolysis of from about 70% to about 100%—OH groups; the remainder of the groups are acetates. Additionally, thedegree of hydrolysis is from about 80% to about 100%, more specificallyfrom about 95% to about 99%.

Additionally, copolymers of poly(vinyl alcohol), comprising poly(vinylalcohol) units and comonomer units, may be used. Suitable comonomerunits for the poly(vinyl alcohol) copolymers include, but are notlimited to, ethylene, methyl acrylate, methyl methacrylate, acrylicacid, itaconic acid, maleic acid, fumaric acid, methyl vinyl ether,propylene, 1-butene, and mixtures thereof. Preferably, the copolymercomprises between about 1 mole percent and about 25 mole percent of thecomonomer relative to the vinyl alcohol units.

The poly(vinyl alcohols) and the poly(vinyl alcohol) copolymers can bederivatized with acetoacetate groups by reaction with diketene, asdescribed by Arthur in U.S. Patent Application Publication No.2006/0079599 (in particular, paragraphs 112-113 and Examples 1-3).Alternative methods of synthesis, such as ester exchange with t-butylacetoacetate, may also be used. Preferably, the acetoacetate derivativeshave an equivalent weight per acetoacetate group of about 100 Daltons toabout 2,000 Daltons.

(iii) Polysaccharides Derivatized with Acetoacetate Groups

The polysaccharides described above can also be derivatized withacetoacetate groups by reaction with diketene. For example, thepreparation of dextran acetoacetate by reaction of dextran with diketeneis described in detail in the Reagent Preparation section of the Examplebelow.

Water-Dispersible Polymers Having Nucleophilic Groups Poly(vinylalcohol) or Poly(vinyl alcohol) Copolymers Having Primary Amine Groups

Poly(vinyl alcohol) and the poly(vinyl alcohol) copolymers describedabove may also be derivatized with primary amine groups using methodsknown in the art, such as those described by Goldmann (U.S. PatentApplication Publication No. 2005/0002893). Additionally, a copolymer ofpoly(vinyl alcohol) and vinyl amine, which can be prepared as describedin the Reagent Preparation section of the Examples below, can be used asa water-dispersible polymer having nucleophilic groups.

Polysaccharides Having Primary Amine Groups

Polysaccharides containing primary amine groups can be prepared bychemical derivatization of a polysaccharide described above usingmethods known in the art. For example, a polysaccharide can be oxidizedto produce an oxidized polysaccharide containing aldehyde groups, asdescribed above. Then, the oxidized polysaccharide can be reacted with adiamine, such as hexamethylene diamine, ethylene diamine, propylenediamine, and the like, to form Schiff base linkages. Optionally, theSchiff base linkages may be treated with a reducing agent such as sodiumborohydride to form stable carbon-nitrogen bonds. Polysaccharidescontaining primary amine groups may also be prepared by reacting apolysaccharide with cyanogen bromide, followed by reaction with adiamine. Additionally, polysaccharides containing primary amine groupscan be prepared by the methods described by Kirakossian et al. (U.S.Pat. No. 7,179,660, Example A). The amine substitution level of thederivatized polysaccharide may be determined using proton NMR.

Preparation of the Fibrous Polymer of Component 1

The fibrous polymer comprises at least one water-dispersible polymerhaving electrophilic groups or nucleophilic groups, as described above.The water-dispersible polymer(s) can be spun into a fibrous polymer thatcomprises the first component of the anhydrous fibrous sheet disclosedherein using solution spinning methods known in the art, such aselectrospinning, electro-blown spinning, or high speed rotary sprayerspinning.

Electrospinning is a well known method for spinning fiber-formingpolymers into fibers (see for example, Chu et al., U.S. Pat. No.7,172,765). Generally, a spinning solution containing a fiber-formingpolymer is introduced through a nozzle into an electric field, which isformed by applying a voltage between the nozzle and a grounded target.The spinning solution exits the nozzle in the form of droplets that areattenuated into fibers by the electric field. The fibers are collectedon the grounded target.

Electro-blown spinning, described by Kim et al., (U.S. PatentApplication Publication No. 2005/0067732), is similar toelectrospinning, but utilizes the combination of an electric field andgas flow to form fibers. Specifically, a concentric airflow is providedaround the outside of the nozzle to attenuate, collimate and direct thefibers to the target. The spinning solution exits the nozzle in the formof droplets that are attenuated into fibers by the air stream and theelectric field.

In high speed rotary sprayer spinning, described by Marshall et al.(U.S. Patent Application Publication No. 2008/0029617), a spinningsolution containing a fiber-forming polymer is supplied to a rotarysprayer having a rotating conical nozzle, which has a concave innersurface and a forward surface discharge edge. The spinning solutionflows out of the rotary sprayer along the concave inner surface so as todistribute the spinning solution toward the forward surface of thedischarge edge of the nozzle, thereby forming separate fibrous streamsfrom the spinning solution while the solvent evaporates to producepolymeric fibers in either the absence or presence of an electric field.

In one embodiment, the fibrous polymer is prepared using electro-blownspinning, as described in the Examples herein. Briefly, at least onewater-dispersible polymer having electrophilic or nucleophilic groups isdissolved in a suitable solvent to prepare a spinning solution. Amixture of water-dispersible polymers having electrophilic groups or amixture of water-dispersible polymers having nucleophilic groups may beused. The solvent may be any solvent which is capable of dissolving thewater-dispersible polymer and providing a fluid capable of beingelectro-blown spun. Suitable solvents include, but are not limited to,water, N,N-dimethylformamide (DMF), tetrahydrofuran (THF), N,N-dimethylacetamide, methylene chloride, dioxane, ethanol, chloroform, andmixtures thereof. In one embodiment, the solvent is water. Theconcentration of the water-dispersible polymer in the spinning solutionis about 1% to about 80%, in more specifically about 10% to about 60% byweight relative to the total weight of the solution. The optimumconcentration to be used can be readily determined by one skilled in theart using routine experimentation. Typically, the spinning solution hasa viscosity of about 50 mPa·s (millipascal-seconds) to about 2,000mPa·s. An inert polymer, such as an unmodified polysaccharide orpolyether, having a high molecular weight (e.g., 100,000 Da) may beadded to the spinning solution if the molecular weight of thewater-dispersible polymer having electrophilic groups or nucleophilicgroups is too low to provide a viscosity sufficient for spinning.

The spinning solution may optionally contain a salt which creates anexcess charge effect to facilitate the electro-blown spinning process.Suitable salts include, but are not limited to, sodium chloride,potassium chloride, magnesium chloride, calcium chloride, potassiumdihydrogen phosphate, potassium monohydrogen phosphate, sodiumbicarbonate, and mixtures thereof.

The spinning solution may further comprise various additives dependingon the intended application. The amount of the additive used depends onthe particular application and may be readily determined by one skilledin the art using routine experimentation. For example, the spinningsolution may comprise at least one additive selected from the groupconsisting of pH modifiers, viscosity modifiers, colorants, surfactants,pharmaceutical drugs and therapeutic agents.

The spinning solution may optionally include at least one pH modifier toadjust the pH of the solution. Suitable pH modifiers are well known inthe art. The pH modifier may be an acidic or basic compound. Examples ofacidic pH modifiers include, but are not limited to, carboxylic acids,inorganic acids, and sulfonic acids. Examples of basic pH modifiersinclude, but are not limited to, hydroxides, alkoxides,nitrogen-containing compounds other than primary and secondary amines,and basic carbonates and phosphates.

The spinning solution may optionally include at least one thickener. Thethickener may be selected from among known viscosity modifiers,including, but not limited to, polysaccharides and derivatives thereof,such as dextran, starch or hydroxyethyl cellulose.

The spinning solution may optionally include at least one antimicrobialagent. Suitable antimicrobial preservatives are well known in the art.Examples of suitable antimicrobials include, but are not limited to,alkyl parabens, such as methylparaben, ethylparaben, propylparaben, andbutylparaben; triclosan; chlorhexidine; cresol; chlorocresol;hydroquinone; sodium benzoate; and potassium benzoate.

The spinning solution may also optionally include at least one colorantto enhance the visibility of the solution and the resulting fibrouspolymer. Suitable colorants include dyes, pigments, and natural coloringagents. Examples of suitable colorants include, but are not limited to,FD&C and D&C colorants, such as FD&C Violet No. 2, FD&C Blue No. 1, D&CGreen No. 6, D&C Green No. 5, D&C Violet No. 2; and natural colorantssuch as beetroot red, canthaxanthin, chlorophyll, eosin, saffron, andcarmine.

The spinning solution may also optionally include at least onesurfactant. Surfactant, as used herein, refers to a compound that lowersthe surface tension of water. The surfactant may be an ionic surfactant,such as sodium lauryl sulfate, or a neutral surfactant, such aspolyoxyethylene ethers, polyoxyethylene esters, and polyoxyethylenesorbitan.

Additionally, the spinning solution may optionally include at least onepharmaceutical drug or therapeutic agent. Suitable drugs and therapeuticagents are well known in the art (for example see the United StatesPharmacopeia (USP), Physician's Desk Reference (Thomson Publishing), TheMerck Manual of Diagnosis and Therapy 18th ed., Mark H. Beers and RobertBerkow (eds.), Merck Publishing Group, 2006; or, in the case of animals,The Merck Veterinary Manual, 9th ed., Kahn, C.A. (ed.), Merck PublishingGroup, 2005). Nonlimiting examples include anti-inflammatory agents, forexample, glucocorticoids such as prednisone, dexamethasone, budesonide;non-steroidal anti-inflammatory agents such as indomethacin, salicylicacid acetate, ibuprofen, sulindac, piroxicam, and naproxen;anti-coagulants such as heparin; peptides; antibacterial agents;antiviral agents; antifungal agents; anti-cancer agents; healingpromoters; adhesion promoters; vaccines; and thrombogenic agents such asthrombin, fibrinogen, heparin binding molecules and/or peptide sequencessuch as HIP peptide, factor VII, factor XIIIa, molecules to stabilizeclot formation via endogenous or exogenous factor XIIIa, such asmolecules containing glutamine and/or lysine residues.

The spinning solution may be spun into a fibrous polymer using anelectro-blown spinning apparatus, containing a metal tube, also referredto as a spinneret, which is charged relative to a grounded target. Thevoltage applied between the metal tube and the grounded target istypically in the range of about 30 to about 100 kilovolts (kV), in morespecifically about 70 to about 100 kV. The spinning solution is pumpedthrough a metal tube with an inside diameter typically of 0.01 to 0.03inches (0.254 to 0.762 mm) at a feed rate appropriate to the solutionviscosity and wt % solids content, typically about 0.1 to about 2.0milliliters per minute. A concentric airflow is provided around theoutside of the metal tube to attenuate, collimate and direct the fibersto the target. The spinning solution exits the metal tube in the form ofdroplets that are attenuated into fibers by the air stream and theelectric field. The fiber may be deposited onto a support fabric, suchas a REEMAY® spunbound polyester fabric, positioned over the target toreceive the spun fiber. The spinning unit may be contained in a spinningchamber, such as a polymethacrylate or polycarbonate box, in which thetemperature and humidity are controlled. Typically, the humidity in thespinning chamber is maintained at about 10% to about 50% at atemperature of about 25° C. to about 50° C.

Second Component

The second component of the anhydrous fibrous sheet disclosed hereincomprises at least one water-dispersible polymer having electrophilicgroups or nucleophilic groups, which is capable of crosslinking thefirst component when the sheet is exposed to an aqueous medium, therebyforming a crosslinked hydrogel that is adhesive to biological tissue.Specifically, if the first component is the fibrous form of awater-dispersible polymer having electrophilic groups, the secondcomponent is a water-dispersible polymer having nucleophilic groups thatare capable of reacting with the electrophilic groups of the firstcomponent to form a crosslinked hydrogel. Conversely, if the firstcomponent is the fibrous form of a water-dispersible polymer havingnucleophilic groups, the second component is a water-dispersible polymerhaving electrophilic groups that are capable of reacting with thenucleophilic groups of the first component to form a crosslinkedhydrogel. The second component may be a mixture of differentwater-dispersible polymers having electrophilic groups or nucleophilicgroups capable of crosslinking the first component. The backbonestructure of the second component can be the same as or different fromthat of the fibrous polymer of the first component. The second componentmay have electrophilic groups including, but not limited to, aldehyde,acetoacetate, succinimidyl, and isocyanate. The second component mayhave nucleophilic groups including, but not limited to, primary amine,secondary amine, carboxyhydrazide, acetoacetate, and thiol.

Suitable water-dispersible polymers having electrophilic groups ornucleophilic groups for use as the second component include thosedescribed above for the first component. Additional suitablewater-dispersible polymers having electrophilic groups for use as thesecond component include, but are not limited to, linear or branchedpolyethers derivatized with acetoacetate groups, linear or branchedpolyethers derivatized with aldehyde groups, linear or branchedpolyethers derivatized with isocyanate groups, and linear or branchedpolyethers derivatized with N-hydroxysuccinimidyl ester groups.Additional examples of suitable water-dispersible polymers havingnucleophilic groups for use as the second component include: linear orbranched polyethers derivatized with primary amine or secondary aminegroups, linear or branched polyethers derivatized with thiol groups, andlinear or branched polyethers derivatized with carboxyhydrazide groups.Some examples of these water-dispersible polymers are described below.

Linear or Branched Polyethers Derivatized with Primary Amine Groups

The linear or branched polyethers are water-dispersible polymers havingthe repeat unit [—O—R]—, wherein R is an hydrocarbylene group having 2to 5 carbon atoms. The term “hydrocarbylene group” refers to a divalentgroup formed by removing two hydrogen atoms, one from each of twodifferent carbon atoms, from a hydrocarbon. Useful linear or branchedpolyethers have a number-average molecular weight of about 300 Daltonsto about 100,000 Daltons, more particularly from about 500 Daltons toabout 20,000 Daltons. Suitable examples of linear or branched polyethersinclude, but are not limited to, linear or branched poly(ethyleneoxide), linear or branched poly(propylene oxide), linear or branchedcopolymers of poly(ethylene oxide) and poly(propylene oxide), linear orbranched poly(1,3-trimethylene oxide), linear or branchedpoly(1,4-tetramethylene oxide), star poly(ethylene oxide), combpoly(ethylene oxide), star poly(propylene oxide), comb poly(propyleneoxide), and mixtures thereof. Many linear polyethers are availablecommercially from companies such as Sigma-Aldrich (St Louis, Mo.). Manybranched polyethers are available from companies such as NektarTransforming Therapeutics (Huntsville, Ala.), SunBio,

Inc. (Anyang City, South Korea), NOF Corp. (Tokyo, Japan), or JenKemTechnology (USA, Allen, Tex.). For example, the water-dispersiblepolymer having nucleophilic groups may be a linear or multi-arm branchedpolyether amine. The linear and branched polyethers described above maybe derivatized with primary amine end groups using methods known in theart (see for example, Poly(Ethylene Glycol) Chemistry: Biotechnical andBiomedical Applications, J. Milton Harris, Ed., Plenum Press, NY, 1992,Chapter 22). Preferably, the amine derivatives have an equivalent weightper amine group of about 100 Daltons to about 2,000 Daltons. Examples ofmulti-arm polyether amines include, but are not limited to, dendritic,comb, and star polyethers wherein at least three of the arms areterminated by a primary amine group. The multi-arm polyether amines havea number-average molecular weight of about 450 to about 100,000 Daltons.Suitable examples of water-dispersible, multi-arm polyether aminesinclude, but are not limited to, amino-terminated star, dendritic, orcomb polyethylene oxides; amino-terminated star, dendritic or combpolypropylene oxides; amino-terminated star, dendritic or combpolyethylene oxide-polypropylene oxide copolymers; and polyoxyalkylenetriamines, sold under the trade name Jeffamine® triamines, by HuntsmanLLC. (Houston, Tex.). Examples of star polyethylene oxide amines,include, but are not limited to, various multi-arm polyethylene glycolamines and star polyethylene glycols having 3, 4, 6, or 8 armsterminated with primary amines (referred to herein as 3, 4, 6 or 8-armstar PEG amines, respectively). The 8-arm star PEG amine is availablefrom Nektar Transforming Therapeutics. Examples of suitable Jeffamine®triamines include, but are not limited to, Jeffamine® T-403 (CAS No.39423-51-3), Jeffamine® T-3000 (CAS No. 64852-22-8), and Jeffamine®T-5000 (CAS No. 64852-22-8). In one embodiment, the water-dispersiblemulti-arm polyether amine is an 8-arm polyethylene glycol having eightarms terminated by a primary amine group and having a number-averagemolecular weight of about 10,000 Daltons, which can be prepared asdescribed in the Reagent Preparation section of the Examples below. Inanother embodiment, the water-dispersible multi-arm polyether amine is a4-arm polyethylene glycol having four arms terminated by a primary aminegroup and having a number-average molecular weight of about 2,000Daltons, which can be prepared as described in the Reagent Preparationsection of the Examples below.

These multi-arm polyether amines are either available commercially, asnoted above, or may be prepared using methods known in the art. Forexample, multi-arm polyethylene glycols, wherein at least three of thearms are terminated by a primary amine group, may be prepared by puttingamine ends on multi-arm polyethylene glycols (e.g., 3, 4, 6, and 8-armstar polyethylene glycols, available from Nektar TransformingTherapeutics, SunBio Corp., and NOF Corp.) using the method described byBuckmann et al. (Makromol. Chem. 182:1379-1384, 1981). In that method,the multi-arm polyethylene glycol is reacted with thionyl bromide toconvert the hydroxyl groups to bromines, which are then converted toamines by reaction with ammonia at 100° C. The method is broadlyapplicable to the preparation of other multi-arm polyether amines.Additionally, multi-arm polyether amines may be prepared from multi-armpolyols using the method described by Chenault (copending and commonlyowned U.S. Patent Application Publication No. 2007/0249870). In thatmethod, the multi-arm polyether is reacted with thionyl chloride toconvert the hydroxyl groups to chlorine groups, which are then convertedto amines by reaction with aqueous or anhydrous ammonia. Other methodsthat may be used for preparing multi-arm polyether amines are describedby Merrill et al. in U.S. Pat. No. 5,830,986, and by Chang et al. in WO97/30103.

The multi-arm amine may also be a multi-arm branched end amine, asdescribed by Arthur (copending and commonly owned Patent Application No.PCT/US07/24393, WO 2008/066787). The multi-arm branched end amines arebranched polymers having two or three primary amine groups at the end ofeach of the polymer arms. The multiplicity of functional groupsincreases the statistical probability of reaction at a given chain endand allows more efficient incorporation of the molecules into a polymernetwork. The starting materials used to prepare the multi-arm branchedend amines are branched polymers such as multi-arm polyether polyolsincluding, but not limited to, comb and star polyether polyols. Thebranched end amines can be prepared by attaching multiple amine groupsto the end of the polymer arms using methods well known in the art. Forexample, a multi-arm branched end amine having two primary aminefunctional groups on the end of each of the polymer arms can prepared byreacting the starting material, as listed above, with thionyl chloridein a suitable solvent such as toluene to give the chloride derivative,which is subsequently reacted with tris(2-aminoethyl)amine to give themulti-arm branched end reactant having two amine groups at the end ofthe polymer arms. In one embodiment, the water-dispersible multi-armamine is an 8-arm polyethylene glycol hexadecaamine having anumber-average molecular weight of about 40,000 Daltons, which can beprepared as described in the Reagent Preparation section of the Examplesbelow.

It should be recognized that the multi-arm polyether amines aregenerally a somewhat heterogeneous mixture having a distribution of armlengths and in some cases, a distribution of species with differentnumbers of arms. When a multi-arm amine has a distribution of specieshaving different numbers of arms, it can be referred to based on theaverage number of arms in the distribution. For example, in oneembodiment the multi-arm amine is an 8-arm star PEG amine, whichcomprises a mixture of multi-arm star PEG amines, some having less thanand some having more than 8 arms; however, the multi-arm star PEG aminesin the mixture have an average of 8 arms. Therefore, the terms “8-arm”,“6-arm”, “4-arm” and “3-arm” as used herein to refer to multi-armamines, should be construed as referring to a heterogeneous mixturehaving a distribution of arm lengths and in some cases, a distributionof species with different numbers of arms, in which case the number ofarms recited refers to the average number of arms in the mixture.

Additionally, other multi-arm amines, such as amino-terminated dendriticpolyamidoamines, sold under the trade name Starburst® Dendrimers(available from Sigma-Aldrich, St Louis, Mo.), may be used aswater-dispersible polymers having nucleophilic groups.

Linear or Branched Polyethers Derivatized with Secondary Amine Groups

Many of the principles described above for the preparation of polymersfunctionalized with primary amines also pertain to the preparation ofpolymers bearing secondary amine groups. For instance the method ofChenault (U.S. Patent Application Publication No. 2007/0249870)referenced above can be adapted by using a mono-substituted amine (e.g.,methylamine) rather than ammonia as a reactant.

Linear or Branched Polyethers Derivatized with Thiol Groups

The water-dispersible polymer having nucleophilic groups may also be alinear or multi-arm polyether thiol. The linear and branched polyethersdescribed above may be derivatized with thiol groups using methods knownin the art involving conversion of the polyether hydroxy ends totoluenesulfonate ends and subsequent reaction with sodium hydrosulfideto give thiol ends (see for example, Harris et al, ACS Polymer Preprints32:154, (1991)). Preferably, the thiol derivatives have an equivalentweight per thiol group of about 100 Daltons to about 2,000 Daltons andhave a number-average molecular weight of about 300 to about 100,000Daltons. Examples of multi-arm polyether thiols include, but are notlimited to, dendritic, comb, and star polyethers wherein at least threeof the arms are terminated by a thiol group.

Linear or Branched Polyethers Derivatized with Carboxyhydrazide Groups

The water-dispersible polymer having nucleophilic groups may also be alinear or multi-arm polyether carboxyhydrazide. The linear and branchedpolyethers described above may be derivatized with carboxyhydrazidegroups using methods known in the art involving conversion of thepolyether hydroxy ends to ethyl acetourethane ends via reaction withethyl isocyanatoacetate followed by reaction with hydrazine to givecarboxyhydrazide ends (see for example, Poly(Ethylene Glycol): Chemistryand Biological Applications, J. Milton Harris et al, Eds., ACS SymposiumSeries 680, NY, 1997, Chapter 21). Preferably, the carboxyhydrazidederivatives have an equivalent weight per carboxyhydrazide group ofabout 100 Daltons to about 2,000 Daltons and have a number-averagemolecular weight of about 300 to about 100,000 Daltons. Examples ofmulti-arm polyether carboxyhydrazides include, but are not limited to,dendritic, comb, and star polyethers wherein at least three of the armsare terminated by a carboxyhydrazide group.

Linear or Branched Polyethers Derivatized with Acetoacetate Groups

The water-dispersible polymer having electrophilic groups may be alinear or multi-arm polyether acetoacetate. The linear and branchedpolyethers may be derivatized with acetoacetate groups by reaction withdiketene, as described by Arthur in U.S. Patent Application PublicationNo. 2006/0079599. Preferably, the acetoacetate derivatives have anequivalent weight per acetoacetate group of about 100 Daltons to about2,000 Daltons and have a number-average molecular weight of about 300 toabout 100,000 Daltons. Examples of multi-arm polyether acetoacetatesinclude, but are not limited to, dendritic, comb, and star polyetherswherein at least three of the arms are terminated by an acetoacetategroup.

Linear or Branched Polyethers Derivatized with Aldehyde Groups

The water-dispersible polymer having electrophilic groups may be alinear or multi-arm polyether aldehyde. The linear and branchedpolyethers described above may be derivatized with aldehyde groups usingmethods known in the art. For example, the primary hydroxy-ended linearand branched polyethers may be converted to toluenesulfonate ends,reacted with sodium hydrosulfide to give thiol ends and subsequentlyreacted with 3-chloropropionaldehyde diethyl acetal followed byhydrolysis to give thiol-linked aldehyde ends (Harris et al., ACSPolymer Preprints 32:154 (1991)). Another polyether aldehyde synthesisis described by Harris (Poly(Ethylene Glycol) Chemistry: Biotechnicaland Biomedical Applications, J. Milton Harris, Ed., Plenum Press, NY,1992, Chapter 22). Alternatively, a polyether functionalized withaldehyde groups can be prepared by reacting primary hydroxy-ended linearand branched polyethers with thionyl chloride to give a polyether havingchloride ends, reacting the chloride-ended polyether with 1-thioglycerolin the presence of a base to yield athiomethylethyleneglycol-functionalized polyether, which is subsequentlyoxidized with an oxidizing agent such as periodate to give athiomethylaldehyde polyether, as described in detail in the ReagentPreparation section of the Examples herein. Additionally, polyethyleneglycols derivatized with aldehyde groups are available from commercialsources, such as Nektar Transforming Therapeutics. Preferably, thealdehyde derivatives have an equivalent weight per aldehyde group ofabout 100 Daltons to about 2,000 Daltons and have a number-averagemolecular weight of about 300 to about 100,000 Daltons. Examples ofmulti-arm polyether aldehydes include, but are not limited to,dendritic, comb, and star polyethers wherein at least three of the armsare terminated by an aldehyde group.

Linear or Branched Polyethers Derivatized with N-HydroxysuccinimidylEster Groups

The water-dispersible polymer having electrophilic groups may also be alinear or multi-arm polyether N-hydroxysuccinimidyl ester. The linearand branched polyethers described above may be derivatized withN-hydroxysuccinimidyl ester groups using methods known in the artinvolving conversion of the polyether hydroxy ends to carboxylic acidsby carboxymethylation followed by reaction with a combination ofN-hydroxysuccinimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimideHCl (EDC) (see for example, Poly(Ethylene Glycol) Chemistry:Biotechnical and Biomedical Applications, J. Milton Harris, Ed., PlenumPress, NY, 1992, Chapter 21), Preferably, the N-hydroxysuccinimidylester derivatives have an equivalent weight per N-hydroxysuccinimidylester group of about 100 Daltons to about 2,000 Daltons and have anumber-average molecular weight of about 300 to about 100,000 Daltons.The multi-arm polyether N-hydroxysuccinimidyl esters include, but arenot limited to, dendritic, comb, and star polyethers wherein at leastthree of the arms are terminated by a N-hydroxysuccinimidyl ester group.

Linear or Branched Polyethers Derivatized with Isocyanate Groups

The water-dispersible polymer having electrophilic groups may also be alinear or multi-arm polyether having isocyanate groups. The linear orbranched polyethers described above may be derivatized with isocyanategroups using methods known in the art (e.g., Zavatsky, U.S. PatentApplication Publication No. 2008/0039548). For example, a linear PEGdiisocyanate can be made by converting the PEG bis(carboxymethyl ether)to the corresponding bis(acyl chloride) which is converted to thebis(acyl azide) and thermally rearranged to the diisocyanate, asdescribed in detail in the Reagent Preparation section of the Examplesbelow.

Combinations of Components

Nonlimiting examples of useful combinations of water-dispersiblepolymers for the first and second components are given below. Othercombinations of water-dispersible polymers having electrophilic groupsand water-dispersible polymers having nucleophilic groups that are knownin the art are also contemplated to be within the scope of theinvention. If the first component is an oxidized polysaccharidecontaining aldehyde groups, (e.g., oxidized dextran); a poly(vinylalcohol) or poly(vinyl alcohol) copolymer derivatized with acetoacetategroups; or a polysaccharide derivatized with acetoacetate groups, thesecond component may be a linear or branched polyether derivatized withprimary amine groups or carboxyhydrazide groups, a polysaccharide havingamine groups, a poly(vinyl alcohol) or a poly(vinyl alcohol) copolymerhaving amine groups. If the first component is a poly(vinyl alcohol) orpoly(vinyl alcohol) copolymer derivatized with acetoacetate groups; or apolysaccharide derivatized with acetoacetate groups, the secondcomponent may also be a linear or branched polyether derivatized withsecondary amine groups, a polysaccharide derivatized with secondaryamine groups, or a poly(vinyl alcohol) or a poly(vinyl alcohol)copolymer derivatized with secondary amine groups. If the firstcomponent is a poly(vinyl alcohol) or poly(vinyl alcohol) copolymerhaving primary amine groups or carboxyhydrazide groups; or apolysaccharide having primary amine groups or carboxyhydrazide groups,the second component may be an oxidized polysaccharide containingaldehyde groups (e.g. oxidized dextran); a poly(vinyl alcohol) orpoly(vinyl alcohol) copolymer derivatized with acetoacetate groups; apolysaccharide derivatized with acetoacetate groups; or a linear orbranched polyether derivatized with acetoacetate groups, aldehydegroups, isocyanate groups, or N-hydroxysuccinimidyl groups. If the firstcomponent is a poly(vinyl alcohol) or poly(vinyl alcohol) copolymerhaving secondary amine groups; or a polysaccharide having secondaryamine groups, the second component may be a poly(vinyl alcohol) orpoly(vinyl alcohol) copolymer derivatized with acetoacetate groups; apolysaccharide derivatized with acetoacetate groups; or a linear orbranched polyether derivatized with acetoacetate groups, isocyanategroups, or N-hydroxysuccinimidyl groups. If the first component is apoly(vinyl alcohol) or poly(vinyl alcohol) copolymer having thiol groupsor a polysaccharide having thiol groups, the second component may be alinear or branched polyether derivatized with N-hydroxysuccinimidylgroups.

In yet another embodiment, the first component is a fibrous polymercomprising an oxidized polysaccharide having aldehyde groups such asoxidized dextran and the second component comprises a multi-armpolyether amine, such as an 8-arm or 4-arm PEG amine, or an 8-arm PEGhexadecaamine.

In yet another embodiment, the first component is a fibrous polymercomprising a poly(vinyl alcohol-co-vinyl amine) and the second componentcomprises a 4-arm PEG thiomethylaldehyde or a linear PEGbis(thiomethylaldehyde).

In another embodiment, the first component is a fibrous polymercomprising oxidized dextran and the second component comprises dextranacetoacetate. In this embodiment, the two polymers are combined in asingle solution and are electro-blown spun to afford fibers containingboth components which are unreactive until activated. The anhydrousfibrous sheet comprising the first and second components is treated withan aqueous base solution to effect dissolution and crosslinking of thehydrogel via condensation of the nucleophilic conjugate base ofacetoacetate with the electrophilic dextran aldehyde groups.

In yet another embodiment, the first component is a fibrous polymercomprising oxidized dextran and the second component comprisespoly(vinyl alcohol-co-vinyl amine).

In another embodiment, the first component is a fibrous polymercomprising a poly(vinyl alcohol) or poly(vinyl alcohol) copolymer havingprimary amine groups, such as poly(vinyl alcohol-co-vinyl amine), andthe second component comprises a linear or branched polyetherderivatized with isocyanate groups, such as a linear PEG diisocyanate.

The second component may be present in the anhydrous fibrous sheet invarious forms. For example, in one embodiment the second component ispresent as a second fibrous polymer, prepared using the methodsdescribed above for the first component, and spun as a second layer ontop of the first fibrous polymer layer. In another embodiment, thesecond component is a fibrous polymer that is cospun from a secondspinning solution through a separate spinning orifice, simultaneouslywith the first component to form a fibrous sheet with intermingledfibers of both components.

In another embodiment, the second component is a coating on the fibrouspolymer of the first component. In this embodiment, the second componentis dissolved in a suitable solvent that dissolves the second component,but does not dissolve the fibrous polymer comprising the firstcomponent, The fibrous polymer is coated with the solution of the secondcomponent using methods known in the art, for example, applying thesolution to the fibrous polymer using a delivery device such as apipette, dip coating, spray coating, and the like. The coated fibrouspolymer is dried to remove the solvent, thereby forming the anhydrousfibrous sheet.

In another embodiment, the second component is a dry powder that isdispersed and entrapped within the interstices of the web of fibrouspolymer of the first component.

For use in medical applications it is preferred that the anhydrousfibrous sheet disclosed herein be sterilized to prevent infection.Suitable sterilization methods include, but are not limited to, gammairradiation, electron beam irradiation, and ultraviolet irradiation.

Various additives may be incorporated into the anhydrous fibrous sheet.Any of the additives described above may be used. The additive may becoated onto the anhydrous fibrous sheet using coating methods well knownin the art. Additionally, a dry powder additive may be dispersed andentrapped within the interstices of the web of fibrous polymer of thefirst component or the second component, if present as a fibrouspolymer. Alternatively, the additive may be covalently coupled to theanhydrous fibrous sheet through the electrophilic or nucleophilic groupspresent on the first and/or second component.

The anhydrous fibrous sheet may also comprise a non-stick coating on atleast one surface to allow convenient application of the fibrous sheetto tissue, so as to prevent, for example, the surgeon's glove frombecoming adherent to the sealant patch. The coating may comprise asilicone, such as polydimethylsiloxane, polyethylene glycols, fattyacids, and polysaccharides such as dextran.

The anhydrous fibrous sheet may also comprise a non-biodegradable,peelable backing to aid in the application of the fibrous sheet totissue. The non-biodegradable backing may be a solid sheet or filmcomprising one or more layers comprised of polymers such aspolytetrafluoroethylene or copolymers thereof, polyethylene,polyacrylate, polyester, polyurethane, nylon, polydimethysiloxane, andthe like. These films may be constructed as is typically done forrelease sheets and/or for barrier-layer films for packagingapplications, including metalized polymer films. The non-biodegradablebacking is removed after application of the anhydrous fibrous sheet tothe tissue site.

The anhydrous fibrous sheet may also comprise a biodegradable, backingto aid in the application of the fibrous sheet to tissue. Thebiodegradable backing may be a sheet or film comprising a biodegradablepolymer such as for example, a polymer comprising one or more monomersselected from the group consisting of a glycolide, lactide, lactic acid,dioxanone, caprolactone, trimethylene carbonate, ethylene glycol,propylene glycol, and lysine. Additionally, various biodegradable,adhesion prevention films, such as oxidized regenerated cellulose (forexample Interceed® absorbable adhesion barrier, available form Ethicon,Inc., Raleigh, N.C.) sodium hyaluronate/carboxymethylcellulose (forexample Seprafilm® adhesion barrier available from Genzyme, Cambridge,Mass.), gelatin, collagen, polyvinyl alcohol, and chitosan film may beused as the biodegradable backing.

Medical Applications of the Fibrous Tissue Sealant

The fibrous tissue sealant, disclosed herein, may be useful as a generaltissue adhesive for medical and veterinary applications including, butnot limited to, wound closure, supplementing or replacing sutures orstaples in internal surgical procedures such as intestinal anastomosisand vascular anastomosis, tissue repair, and to prevent post-surgicaladhesions. The fibrous tissue sealant may be particularly suitable foruse as a hemostat to stanch bleeding from surgical or traumatic wounds.

In one embodiment, the fibrous tissue sealant is used to apply a coatingto an anatomical site on tissue of a living organism. The coating mayact as a sealant or adhesive, or as an antiadhesive coating to preventpost-surgical adhesions. To apply the coating, the anhydrous fibroussheet disclosed herein is applied to the site and the first and secondcomponents are hydrated and allowed to crosslink at the site to form ahydrogel that is adhesive to tissue. The fibrous sheet may be applied tothe site in various ways, such as using gloved fingers, sterile forceps,or other sterile applicator. The fibrous sheet may be hydrated by bodyfluids present at the site or by the addition an aqueous medium, such asan aqueous buffer solution.

In another embodiment, the fibrous tissue sealant is used to stanchbleeding from a surgical or traumatic wound in tissue of a livingorganism. In this embodiment, the anhydrous fibrous sheet disclosedherein is applied to the site of the wound and allowed to hydrate byabsorbing blood, whereby the first component and the second componentcrosslink to form a hydrogel that is adhesive to tissue.

In another embodiment, a coating is applied to an anatomical site ontissue of a living organism by applying the fibrous polymer of the firstcomponent to the site, applying the second component in the form of anaqueous solution or dispersion to the site, and allowing the first andthe second component to crosslink on the site, thereby forming ahydrogel that is adhesive to the tissue. The aqueous solution ordispersion comprises from about 5% to about 70% by weight of the secondcomponent relative to the total weight of the aqueous solution ordispersion. The aqueous solution or dispersion may be applied to thesite in a variety of ways, for example, applying with a syringe or spraydevice.

EXAMPLES

The present invention is further defined in the following Examples. Itshould be understood that these Examples, while indicating preferredembodiments of the invention, are given by way of illustration only.From the above discussion and these Examples, one skilled in the art canascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various uses andconditions.

A reference to “Aldrich” or a reference to “Sigma” means the saidchemical or ingredient was obtained from Sigma-Aldrich, St. Louis, Mo.

Reagent Preparation Preparation of Dextran Aldehyde (D10-50)

Dextran aldehyde having an average molecular weight of about 10 kDa anda degree of oxidation of about 50%, referred to herein as D10-50, ismade by oxidizing dextran in aqueous solution with sodium metaperiodate.An oxidized dextran with about 50% oxidation conversion (i.e., abouthalf of the glucose rings in the dextran polymer were oxidized todialdehydes) is prepared from dextran having a weight-average molecularweight of 8,500 to 11,500 Daltons (Sigma) by the method described byCohen et al. (copending and commonly owned Patent Application No.PCT/US08/05013). A typical procedure is described here.

A 20-L reactor equipped with a mechanical stirrer, addition funnel,internal temperature probe, and nitrogen purge is charged with 1000 g ofthe dextran and 9.00 L of de-ionized water. The mixture is stirred atambient temperature to dissolve the dextran and then cooled to 10 to 15°C. To the cooled dextran solution is added over a period of an hour,while keeping the reaction temperature below 25° C., a solution of 1000g of sodium periodate dissolved in 9.00 L of de-ionized water. Once allthe sodium periodate solution has been added, the mixture is stirred at20 to 25° C. for 4 more hours. The reaction mixture is then cooled to 0°C. and filtered to clarify. Calcium chloride (500 g) is added to thefiltrate, and the mixture is stirred at ambient temperature for 30 minand then filtered. Potassium iodide (400 g) is added to the filtrate,and the mixture is stirred at ambient temperature for 30 min. A 3-Lportion of the resulting red solution is added to 9.0 L of acetone overa period of 10 to 15 min with vigorous stirring by a mechanical stirrerduring the addition. After a few more minutes of stirring, theagglomerated product is separated from the supernatant liquid. Theremaining red solution obtained by addition of potassium iodide to thesecond filtrate is treated in the same manner as above. The combinedagglomerated product is broken up into pieces, combined with 2 L ofmethanol in a large stainless steel blender, and blended until the solidbecomes granular. The granular solid is recovered by filtration anddried under vacuum with a nitrogen purge. The granular solid is thenhammer milled into a fine powder. A 20-L reactor is charged with 10.8 Lof de-ionized water and 7.2 L of methanol, and the mixture is cooled to0° C. The granular solid formed by the previous step is added to thereactor and the slurry is stirred vigorously for one hour. Stirring isdiscontinued, and the solid is allowed to settle to the bottom of thereactor. The supernatant liquid is decanted by vacuum, 15 L of methanolis added to the reactor, and the slurry is stirred for 30 to 45 minwhile cooling to 0° C. The slurry is then filtered in portions, and therecovered solids are washed with methanol, combined, and dried undervacuum with a nitrogen purge to give about 600 g of the oxidizeddextran, which is referred to herein as D10-50.

The degree of oxidation of the product is determined by proton NMR to beabout 50% (equivalent weight per aldehyde group=146). In the NMR method,the integrals for two ranges of peaks are determined, specifically,—O₂CHx- at about 6.2 parts per million (ppm) to about 4.15 ppm (minusthe HOD peak) and —OCHx- at about 4.15 ppm to about 2.8 ppm (minus anymethanol peak if present). The calculation of oxidation level is basedon the calculated ratio (R) for these areas, specifically,R═(OCH)/(O₂CH).

Preparation of Dextran Aldehyde (D100-6)

Dextran aldehyde having an average molecular weight of about 100 kDa anda degree of oxidation of about 6%, referred to herein as D100-6, is madeby oxidizing dextran in aqueous solution with sodium metaperiodate. Anoxidized dextran with about 5-10% oxidation (i.e., about 5-10% of theglucose rings in the dextran polymer were oxidized to dialdehydes) isprepared from dextran having a weight-average molecular weight of100,000 to 200,000 Daltons (Sigma). A solution of 2.0 g sodium periodatein 15 mL of deionized water is added all at once with stirring to asolution of 22 g dextran D100 (Sigma D4876; Mw=100-200 kDa) in 150 mL ofdeionized water and the solution is stirred for 4 hours at roomtemperature. After 4 hours, 1 mL of ethylene glycol is added to thereaction to destroy any remaining periodate and the solution is stirredfor 15 min more. Then 1 g of calcium chloride dihydrate is added and thesolution is magnetically stirred in an ice bath for 1 hour and thensuction-filtered through a coarse frit to remove calcium iodatehexahydrate. The clear filtrate is then combined with 0.5 g of potassiumiodide with magnetic stirring, resulting in a red solution which isstirred at room temperature for 30 min. The solution is poured into 1000mL of acetone and swirled briefly to produce a suspension of swollenliquid dextran aldehyde which coats out on the walls of the flask. Afterstanding for 30 min, the acetone is poured off and the polymer isstirred with a spatula with 200 mL of methanol, which hardens thepolymer. The methanol is decanted off after 10 min and the polymer isblended in a Waring blendor with 500 mL methanol for 5 min. Theresulting suspension is suction-filtered and dried overnight under anitrogen blanket to yield 19.8 g of dextran aldehyde D100-6. The degreeof oxidation of the product is determined by proton NMR to be about 6%(equivalent weight per aldehyde group=1335).

Preparation of Eight-Arm PEG 40K Hexadecaamine (P8-40-2)

Eight-arm PEG 40K (M_(n)=40 kDa) hexadecaamine, having two amino groupson the end of each arm, is synthesized via the reaction of 8-arm PEG 40Kchloride with tris(2-aminoethyl)amine, i.e.,

The 8-arm PEG 40K chloride is made by reaction of thionyl chloride withthe 8-arm PEG 40K octaalcohol. A typical procedure is described here.

A solution of 100 g (20 mmol OH) of 8-arm PEG 40K (M_(n)=40,000; NOFSunBright HGEO-40000) in 200 mL of toluene is heated to 70° C. andstirred under nitrogen as 6 mL of thionyl chloride (10 g; 80 mmol) isquickly added. The mixture is stirred at 60° C. under nitrogen for 20hours, after which the solution is bubbled with nitrogen for 1 hourwhile still warm to remove thionyl chloride and then 2 mL (50 mmol) ofmethanol is added to scavenge remaining thionyl chloride. The resultingsolution is added, with stirring, to 300 mL of hexane to initially makea gelatinous precipitate which soon becomes friable and powdery as thetoluene extracts from the product. The white suspension is stirred foran hour and then suction-filtered on a glass-fritted funnel, washed oncewith 100 mL of hexane and suctioned-dry on the funnel under a nitrogenblanket to yield the 8-arm PEG 40K chloride.

A solution of 30.0 g (6.0 mmol Cl) of 8-arm PEG 40K chloride in 60 mL ofwater is rapidly stirred as 36 mL (35.3 g; 240 mmol) oftris(2-aminoethyl)amine (TCI America, Portland, Oreg.; #T1243) is added.The resulting solution is stirred in a 100° C. oil bath under nitrogenfor 25 hours. Then, 0.5 mL (9 mmol) of 50% sodium hydroxide is added andthe mixture is cooled and extracted with 150 mL of dichloromethanefollowed by 2 extractions with 100 mL portions of dichloromethane.Separation is somewhat slow but is eventually complete overnight. Thecombined extracts are dried with sodium sulfate, evaporated to a volumeof 120 mL using rotary evaporation, and precipitated into 850 mL ofdiethyl ether with stirring. The ether is then stirred in an ice bathand the resulting white precipitate is suction-filtered on aglass-fritted funnel under nitrogen, washed with 100 mL of diethyl etherand suctioned dry on the funnel under nitrogen to yield the 8-arm PEG40K hexadecaamine, referred to herein as P8-40-2.

Proton NMR results from one preparation are:

¹H NMR (500 MHz; CDCl₃): δ 2.53 ppm (t, J=6.0 Hz, a); 2.60 (t, J=6.1 Hz,b); 2.71 (t, J=6.1 Hz, c); 2.76 (t, J=5.9 Hz, d); 2.80 (t, J=5.2 Hz, e);3.59 (t, J=5.3 Hz, f); 3.64 (s, g); 3.76 CH₂Cl (t, 3=6.0 Hz; h; gone).Integrate groups of peaks: 2.5-2.8 ppm (a-e; 14.3H; theory 14H); 3.5-3.8ppm (f-g, PEG backbone, 500H). There is no remainingtris(2-aminoethyl)amine by NMR.

Preparation of Eight-Arm PEG 10K Octaamine (P8-10-1)

Eight-arm PEG 10K octaamine (M_(n)=10 kDa) is synthesized using thetwo-step procedure described by Chenault in co-pending and commonlyowned U.S. Patent Application Publication No. 2007/0249870. In the firststep, the 8-arm PEG 10K chloride is made by reaction of thionyl chloridewith the 8-arm PEG 10K octaalcohol. In the second step, the 8-arm PEG10K chloride is reacted with aqueous ammonia to yield the 8-arm PEG 10Koctaamine. A typical procedure is described here.

The 8-arm PEG 10K octaalcohol (M_(n)=10000; NOF SunBright HGEO-10000),(100 g in a 500-mL round-bottom flask) is dried either by heating withstirring at 85° C. under vacuum (0.06 mm of mercury (8.0 Pa)) for 4 h orby azeotropic distillation with 50 g of toluene under reduced pressure(2 kPa) with a pot temperature of 60° C. The 8-arm PEG 10K octaalcoholis allowed to cool to room temperature and thionyl chloride (35 mL, 0.48mol) is added to the flask, which is equipped with a reflux condenser,and the mixture is heated at 85° C. with stirring under a blanket ofnitrogen for 24 hours. Excess thionyl chloride is removed by rotaryevaporation (bath temp 40° C.). Two successive 50-mL portions of tolueneare added and evaporated under reduced pressure (2 kPa, bath temperature60° C.) to complete the removal of thionyl chloride.

¹H NMR (500 MHz, DMSO-d6) δ 3.71-3.69 (m, 16H), 3.67-3.65 (m, 16H), 3.50(s, ˜800H).

The 8-arm PEG 10K octachloride (100 g) is dissolved in 640 mL ofconcentrated aqueous ammonia (28 wt %) and heated in a pressure vesselat 60° C. for 48 hours. The solution is sparged for 1-2 hours with drynitrogen to drive off 50 to 70 g of ammonia. The solution is then passedthrough a column (500 mL bed volume) of strongly basic anion exchangeresin (Purolite® A-860, The Purolite Co., Bala-Cynwyd, Pa.) in thehydroxide form. The eluant is collected and three 250-mL portions ofde-ionized water are passed through the column and also collected. Theaqueous solutions are combined, concentrated under reduced pressure (2kPa, bath temperature 60° C.) to about 200 g, frozen in portions andlyophilized to give the 8-arm PEG 10K octaamine, referred to herein asP8-10-1, as a colorless waxy solid.

Preparation of Four-Arm PEG 2K Tetraamine (P4-2-1)

A 4-arm PEG 2K (M_(n)=2 kDa) tetraamine is prepared using a similarprocedure as described above for the 8-arm PEG 10K octaamine.

Four-arm PEG 2K tetraalcohol (M_(n)=2000; NOF SunBright PTE-2000), (100g in a 500-mL round-bottom flask) is dissolved in 100 mL ofdichloromethane. Thionyl chloride (88 mL, 1.2 mol) is added, and themixture is stirred under a blanket of nitrogen at ambient temperaturefor 24 hours. Excess thionyl chloride and dichloromethane are removed byrotary evaporation (bath temp 40° C.). Two successive 50-mL portions oftoluene are added and evaporated under reduced pressure (2 kPa, bathtemperature 60° C.) to complete the removal of thionyl chloride.

Proton NMR results from one preparation are:

¹H NMR (500 MHz, DMSO-d6): δ3.71-3.68 (m, 8H), 3.67-3.65 (m, 8H),3.57-3.55 (m, 8H), 3.50 (m, ˜140H), 3.47-3.45 (m, 8H), 3.31 (s, 8H).

The 4-arm PEG 2K tetrachloride (40 g) is dissolved in 600 mL ofconcentrated aqueous ammonia (28 wt %) and heated in a pressure vesselat 60° C. for 48 hours. The solution is cooled and sparged for 1.5 hourswith dry nitrogen, and then concentrated by rotary evaporation (2 kPa,bath temperature 60° C.) to about 500 g. The solution is then passedthrough a column (500 mL bed volume) of strongly basic anion exchangeresin (Purolite® A-860) in the hydroxide form. The eluant is collected,and two 250-mL portions of de-ionized water are passed through thecolumn and collected. The aqueous fractions are combined and evaporatedunder reduced pressure (2 kPa, bath temperature 60° C.) to give the4-arm PEG 2K tetraamine, referred to herein as P4-2-1, as a clear,pale-yellow liquid.

¹H NMR (500 MHz, CDCl₃): δ 3.65-3.51 (m, ˜170H), 3.47 (m, 8H), 3.36 (s,8H), 2.86 (t, 3=5.3 Hz, 7.4H), 2.76 (t, 3=5.4 Hz, 0.6H).

Preparation of Poly(Vinyl Alcohol-Co-Vinyl Amine) Method a

A copolymer of vinyl alcohol and vinyl amine is made by copolymerizingvinyl acetate and N-vinylformamide followed by hydrolysis. A thiol chaintransfer agent is employed to limit polymer molecular weight and providea practical spinning solution viscosity.

A solution of 0.1 g sodium dodecylbenzenesulfonate in 80 mL of deionizedwater is placed in a 250-mL, 4-neck round-bottom flask with condenserand nitrogen inlet, thermometer, 2 dropping funnels and a magneticstirrer. The flask is swept with nitrogen and stirred in a 90° C. oilbath until the solution temperature is 90° C.; then 0.1 g of AIBN(2,2′-azobisisobutyronitrile; Aldrich 441090) initiator is added. Asolution of 32 g vinyl acetate (Aldrich V1503; filtered through basicalumina to remove inhibitor), 5 g N-vinylformamide (Aldrich 447331; asreceived) and 0.10 mL of 2-mercaptoethanol (Aldrich M3701) is placed ina larger dropping funnel under nitrogen, and a solution of 1.0 g AIBN in9 mL of vinyl acetate is placed in a smaller dropping funnel. Fourmilliliters of the thiol-containing monomer solution and 1 mL of theAIBN-containing monomer solution are then added to the flask withstirring and the polymerization proceeds at 90° C. under refluxing vinylacetate (boiling point of 72° C.). The mixture is stirred for 20 min andanother 4 mL+1 mL of the two monomer solutions, respectively, are added,after which the mixture becomes increasingly opaque white. The 4 mL+1 mLof the two monomer solutions are added every 20 min for 1 hour; then themixture is stirred for 1 hour at 90° C. After this time, the remainderof the monomers are added at a rate of 4 mL+1 mL every 20 min. When themonomers are all added (about 4 hours), the mixture is stirred at 90° C.for 2 hours more and then the heating bath is removed. The suspension isrotary evaporated to remove monomer and water and the damp sludge istaken up in 250 mL of methanol. An aliquot is precipitated with diethylether and dried under high vacuum for analysis by proton NMR and sizeexclusion chromatography.

¹H NMR (500 MHz; DMSO-d6): by ratio of the 3.80-ppm N-vinylformamidemethine peak to the 4.78-ppm vinyl acetate methine peak, the polymer has11.2 mol % N-vinylformamide incorporation (hydrolyzed amine EW=390).Size exclusion chromatography (dimethylacetate) results: M_(n)=44,700;M_(w)=447,000; M_(z)=2,086,000; M_(w)/M_(n)=10.0; g′=0.81; α=0.59.

Ten milliliters of concentrated hydrochloric acid is added to themethanol solution of polymer and the resulting mixture is stirred atreflux for 24 hours, during which time a rubbery polymer precipitatesand coagulates. Proton NMR (DMSO-d6) shows that the acetate groups aregone. Filtration and drying under nitrogen yields 18.3 g of thepoly(vinyl alcohol-co-vinyl amine hydrochloride) product. The product isdissolved in 170 mL of deionized water and the resulting solution isfiltered through a 5-μm membrane filter. The filtered solution isbasified to pH 9.0 (measured with a pH electrode) with NaOH and thesolution is desalted by dialysis against deionized water in aMEMBRA-CELL® (Viskase Companies, Inc., Willowbrooke, Ill.) 3.5K MWCO(molecular weight cut-off) dialysis membrane tube. The dialyzedpoly(vinyl alcohol-co-vinyl amine) solution is then adjusted to 20 wt %by rotary evaporation to remove excess water. This polymer solution iskept protected from atmospheric carbon dioxide which would react withthe amine groups to form unreactive carbamates.

Preparation of Poly(Vinyl Alcohol-Co-Vinyl Amine) Method B

A poly(vinyl alcohol-co-vinyl amine) polymer is made using carbontetrachloride as a chain transfer agent rather than mercaptoethanol asin Method A.

A monomer solution of 40.0 g vinyl acetate (Aldrich V1503; filteredthrough alumina to remove inhibitor) and 5.0 g N-vinylformamide (Aldrich447331) is syringe-filtered to remove a small amount of polymer. Then,0.10 g of carbon tetrachloride (0.12 mol % based on monomer) and 0.3 gof AIBN (2,2′-azobisisobutyronitrile; Aldrich 441090) are added to thesolution.

A solution containing 0.1 g of sodium dodecylbenzenesulfonate and 0.1 gof sodium dihydrogen phosphate in 80 mL of deionized water is placed ina 250-mL, 4-neck round-bottom flask with condenser, nitrogen inlet,thermocouple well, monomer inlet line and magnetic stir bar. The flaskis swept with nitrogen and stirred in a 70° C. water bath until thesolution temperature reaches 65° C. Then, 0.1 g of AIBN initiator isadded to the flask, followed immediately by the addition of 5 mL ofmonomer solution with stirring. The remainder of the monomer solution isplaced in a 60-mL syringe on a syringe pump and the solution isdelivered to the flask at a rate of 0.25 mL/min over 3 hours. When themonomer solution has all been added, the mixture is stirred in the 70°C. bath for 1 hour more, and then the heating bath is removed and thesuspension is cooled to 22° C., resulting in the formation of a gooeymixture, which is rotary evaporated to remove vinyl acetate and water.The resulting material is taken up in 50 mL of methanol and the solutionis poured into ice water with stirring to give a congealed soft rubberpolymer. The polymer is worked (masticated by hand) in hot water toremove soap and monomer and then chilled in ice water, forming a stifferpolymer which can be torn apart into fibrils. The polymer is soaked inwater overnight and then filtered and dried under vacuum to yieldpoly(vinyl acetate-co-vinyl formamide).

¹H NMR (500 MHz; DMSO-d6): by ratio of the 3.80-ppm NVF methine peak(1.84) to the 4.77-ppm VAc methine peak (14.45), the polymer has 11.3mol % N-vinylformamide incorporation (hydrolyzed amine EW=390).

Size exclusion chromatography (SEC) Results (DMAc): M_(n)=60,310;M_(w)=202,160; M_(z)=464,260; M_(w)/M_(n)=3.35; [η]=0.62; α=0.51.

The poly(vinyl acetate-co-vinyl formamide) product is stirred in a500-mL resin kettle with 250 mL of methanol and 10 mL (0.1 mol) ofconcentrated hydrochloric acid at reflux for 16 hours. The mixturebecomes a solution in about an hour, and a rubbery polymer begins toseparate at about 6 hours. The rubbery polymer is cut up with scissorsinto 1-cm chunks, washed with methanol and dried under nitrogen on afunnel to yield 30.5 g of rubbery poly(vinyl alcohol-co-vinyl aminehydrochloride) polymer. This polymer is stirred with 100 mL of deionizedwater on a hot plate to give a solution which is then basified to pH 10with 10 wt % NaOH. This solution is dialyzed in a MEMBRA-Cell® (ViskaseCompanies, Inc., Willowbrooke, Ill.) 3.5K MWCO dialysis tube in stirreddeionized water for 24 hours. The water is changed twice in the first 6hours. The top of the bucket containing the water is kept covered withaluminum foil and nitrogen is continuously bubbled through the water inthe bucket to keep carbon dioxide in the air from reacting with theamino polymer. The dialyzed solution is frozen in liquid nitrogen andlyophilized to yield 12.4 g of poly(vinyl alcohol-co-vinyl amine).

It should be noted that thiol chain transfer (Method A) is preferable tocarbon tetrachloride in controlling the molecular weight of thepoly(vinyl acetate-co-vinyl formamide), in that the poly(vinylalcohol-co-vinyl amine) polymers produced using thiols can be dissolvedto a higher percent solids content without forming gels at a givenmolecular weight. Many other chain transfer agents can be used, such asmethanol or isopropanol.

Preparation of Four-Arm PEG 2K Tetra(Thiomethylaldehyde)

A 4-arm PEG 2K tetra(thiomethylaldehyde) is prepared by reacting 4-armPEG 2K tetrachloride with 1-thioglycerol to give a 4-arm PEG 2K withthiomethylethyleneglycol ends. Oxidation of this intermediate with oneequivalent of sodium metaperiodate per glycol group yields the 4-arm PEG2K terminated with thiomethylaldehyde groups.

A solution of 10.0 g (20 mmol Cl) 4-arm PEG 2K tetrachloride, describedabove in the preparation of 4-Arm PEG 2K tetraamine (P4-2-1), 2.5 g (30mmol) sodium bicarbonate and 3.5 g (32 mmol) 1-thioglycerol (AldrichM1753) in 30 mL of water is stirred in a 90° C. oil bath under nitrogenfor 22 hours. The solution is cooled to room temperature and extractedwith three 35 mL portions of dichloromethane. The combined extracts aredried with sodium sulfate followed by magnesium sulfate, filtered,concentrated to 20-25 mL and precipitated with stirring in 500 mL ofdiethyl ether with chilling in ice. The product is still a liquid at 0°C., so stirring is stopped and the flask is cooled in dry ice. The etheris decanted off the white product which has solidified on the bottom ofthe flask. The flask is warmed to room temperature and the liquefiedproduct is stirred with 200 mL of fresh ether and chilled again in dryIce. The ether is decanted off and the product is taken up indichloromethane (50 mL) and transferred to a round-bottom flask. Thesolvent is removed by rotary evaporation and the concentrate is heldunder high vacuum to yield 7.5 g of 4-arm PEG 2Ktetra(thiomethylethyleneglycol) as a clear liquid.

¹H NMR (500 mHz; CDCl₃): δ 2.70 ppm (ABX q of d, 2H, a); 2.76 (t, J=6.1Hz, 2H, b); 3.41 (s, pentaerythritol core CH₂O, 2H); 3.54 (m, 3H, c);3.59 (t, J=4.7 Hz, 2H, d); 3.64 (s, 46H, e); 3.75 (t, CH₂Cl, gone); 3.81(m, 1H, f).

A solution of 2.0 g (3.5 mmol diol; EW approximately equal to 575; M_(n)approximately equal to 2300) 4-arm PEG 2Ktetra(thiomethylethyleneglycol) in 20 mL of deionized water is stirredin an ice bath as a solution of 0.75 g (3.5 mmol) sodium metaperiodatein 10 mL of water is added in 3-mL portions every 5 min. The mixture isallowed to stir at 0° C. for 60 min and then 5 drops of ethylene glycolare added and the solution is extracted with four 25 mL portions ofdichloromethane. The combined extracts are dried with magnesium sulfateand concentrated by rotary evaporation from a warm tap water bath toabout 15 mL. The concentrate is added with stirring to 150 mL of diethylether. The mixture is stirred for 15 min and then cooled in dry ice tofreeze the product. The ether is decanted off, replaced with 100 mL offresh ether and the mixture is warmed to room temperature and stirredfor 10 min, followed by freezing and decanting again. The product isthen taken up in 25 mL of dichloromethane, transferred to a 100-mLround-bottom flask, and rotary evaporated from a warm tap water bath.The concentrate is held under vacuum at 22° C. with a nitrogen bleedthrough a syringe needle to remove solvent, yielding 1.10 g of liquid4-arm PEG 2K tetra(thiomethylaldehyde).

Infrared (neat): 1716 cm-1 (CHO)

¹H NMR (500 MHz; CDCl₃): δ 2.66 ppm (t, J=6.1 Hz, 2H, a); 3.27 ppm (d,3=3.5 Hz, 2H, b); 3.64 ppm (s, 46H, c); 9.51 ppm (t, J=3.3 Hz, 0.8H d).By ratio of the SCH₂CHO integral (9.51 ppm) to S(═O)CH₂CHO integral(9.86 ppm). The product contains about 12 mol % sulfoxide aldehyde endsdue to over-oxidation with excess metaperiodate. This compound isunstable with respect to self-condensation due to the acidic methylenebetween the aldehyde and sulfoxide and therefore is best used promptly.

Preparation of Linear PEG 600 Bis(Thiomethylaldehyde)

A low molecular weight linear PEG bis(thiomethylaldehyde) is made byconverting the PEG diol to the corresponding dichloride, converting thedichloride to the bis(thiomethylethyleneglycol), which is oxidized tothe bis (thiomethylaldehyde).

A solution of 20 g (67 mmol OH) PEG 600 (M_(n)=600; Aldrich 202401) and0.2 mL of N,N-dimethylacetamide in 60 mL of toluene in a 200-mLround-bottom flask is stirred in a 70° C. oil bath as 7.5 mL of thionylchloride (12 g; 100 mmol) is added dropwise down the condenser. Thesolution is stirred under nitrogen at 70° C. for 20 hours. The mixtureis rotary evaporated to remove about half of the toluene. The resultingconcentrate is added to ether chilled in an ice bath, and then chilledin dry ice to separate a slurry which is quickly filtered cold and thenadded to 200 mL of hexane. The resulting solid, which is very sticky andlow-melting, is taken up in dichloromethane, rotary evaporated and heldunder vacuum under a nitrogen stream from a needle through a septum toremove solvent. The resulting PEG 600 dichloride (10.4 g) is a brownoil.

¹H NMR (500 MHz; CDCl₃): δ 3.64 ppm (s, OCH₂CH₂O backbone; 52H); 3.76ppm (t, 3=5.9 Hz, ClCH₂CH₂O; 4H).

A solution of 9.0 g (29 mmol Cl) PEG 600 dichloride, 4.0 g (48 mmol)sodium bicarbonate and 4.3 g (40 mmol) 1-thioglycerol (Aldrich M1753) in25 mL of water is stirred in a 100° C. oil bath under nitrogen for 16hours. The solution is extracted with four-40 mL portions ofdichloromethane. The combined extracts are dried with magnesium sulfate,filtered, concentrated to 20 mL and precipitated from 200 mL of diethylether chilled in an ice bath. The product is still a liquid at 0° C., sostirring is stopped and the flask is cooled in dry ice. The ether isdecanted off the white product which has solidified on the bottom of theflask. The flask is warmed to room temperature and the liquefied productis stirred with 200 mL of fresh ether and chilled again in dry ice. Theether is decanted off and the product is taken up in dichloromethane (50mL) and transferred to a round-bottom flask. The solvent is rotaryevaporated off and the resulting concentrate is held under vacuum with anitrogen purge through a syringe needle to yield 7.4 g of PEG 600bis(thiomethylethyleneglycol).

¹H NMR (500 MHz; CDCl₃): δ 2.71 ppm (ABX q of d, 4H); 2.77 (t, J=6.1 Hz,4H); 3.55 (m, 2H); 3.64 (s, 52H); 3.69 (t, J=6.2 Hz, ˜6H); 3.75 (t,CH₂Cl, gone); 3.83 (m, 2H).

A solution of 6.00 of g (15.8 mmol diol; EW approximately equal to 380;M_(n) approximately equal to 760) PEG 600 bis(thiomethylethyleneglycol)in 30 mL of deionized water is stirred in an ice bath as a solution of3.40 g (16 mmol) sodium metaperiodate in 30 mL of water is added at arate of 1 mL/min using a syringe pump. Following the addition, themixture is allowed to stir at 0° C. for 60 min and then 10 drops ofethylene glycol are added and the solution is extracted with four-40 mLportions of dichloromethane. The combined extracts are dried withmagnesium sulfate and concentrated by roto evaporation from a warm tapwater bath to a volume of about 15 mL. The concentrate is added withstirring to 200 mL of diethyl ether. The mixture is stirred for 15 minand then cooled in dry ice to freeze the product. The ether is decantedoff, replaced with 100 mL of fresh ether and the mixture is warmed toroom temperature and stirred for 10 min, followed by freezing anddecanting again. The product is then taken up in dichloromethane andtransferred to a 100-mL round-bottom flask, rotary evaporated from awarm tap water bath, and then held under vacuum at 22° C. with anitrogen bleed through a syringe needle to remove solvent, yielding 2.0g of PEG 600 bis(thiomethylaldehyde) as an orange liquid.

Infrared (neat): 1716 cm-1 (CHO). This product is stable under nitrogenfor months.

¹H NMR (500 MHz; CDCl₃): δ 2.66 ppm (t, J=6.2 Hz, 4H); 3.27 (d, J=3.3Hz, 4H); 3.64 (s, 88H); 9.51 (t, J=3.3 Hz, 2H); There is <1%over-oxidized sulfoxide aldehyde present.

Preparation of Dextran Acetoacetate

Dextran acetoacetate is prepared by reacting dextran with diketene.Dextran (55 g; Sigma D4876; M_(w)=100-200 kDa) is dried in a vacuum ovenunder a nitrogen stream at 100° C. and 300 mm Hg (40 kPa) for 3 hours. A15.0-g sample of the dried dextran (unit mw=162.14; OH eq wt=54; 278mmol OH) is combined with 160 mL of dry N,N-dimethylacetamide and 0.2 gof N,N-4-dimethylaminopyridine in a 500-mL round-bottom flask undernitrogen. The mixture is purged by bubbling with nitrogen for 5 min andthen is magnetically stirred in a 100° C. oil bath to give acream-colored suspension. To this mixture, 5 g of dry lithium chlorideis added and a clear yellow solution results in about 10 min. Thesolution is cooled and stirred at 22° C. as 6.0 mL (6.5 g; 78 mmol) offreshly sublimated diketene (Aldrich #302058; distilled at 0.4 mm Hg(0.05 kPa) to a liquid nitrogen-cooled cold finger condenser) is addedby syringe over a period of 30 sec. The internal temperature slowlyrises to about 40° C. and then cools. The resulting yellow solution isstirred at 22° C. for 22 hours and then is blended into 700 mL ofmethanol in a Waring® blender (Waring Products, Torrington, Conn.) toafford a blob of soft, taffy-like polymer. The polymer mass is stretchedout and cut into 1-cm pieces with scissors and fed to 500 mL of acetonein a blender. Blending for 15 min results in a suspension of solidparticulate polymer which is suction-filtered on a coarse glass-frittedfunnel and suctioned dry under a nitrogen blanket to yield 17.8 g ofdextran acetoacetate as a water-soluble tan powder.

The acetoacetate content is determined by proton NMR in D₂O. The ratioof the acetoacetate CH₃ peak (2.35 ppm, 3H) with the dextran skeletal CHpeaks (3.4-4.1 ppm and 4.8-5.3 ppm; 7H total per glucose unit) gives adegree of substitution=0.74; equivalent weight per acetoacetategroup=303.

Preparation of Linear PEG 600 Diisocyanate

The PEG 600 diisocyanate is made by converting the PEG 600bis(carboxymethyl ether) to the corresponding bis(acyl chloride) whichis converted to the bis(acyl azide) and thermally rearranged to thediisocyanate.

A solution of 15 g of PEG bis(carboxymethyl ether) (50 mmol COOH;EW=300; Aldrich 407038) and 3 drops of N,N-dimethylacetamide in 40 mL ofdichloromethane is stirred at room temperature in a 100-mL round-bottomflask with a condenser as 8.1 g of thionyl chloride (5.0 mL; 68 mmol) isadded down the condenser. A drying tube is placed on the condenser andthe solution is stirred at reflux for 3 hours. If infra-redspectrospcopic analysis indicates the presence of some remaining COOH(1753 cm⁻¹), an additional 1 mL of thionyl chloride is added and themixture is stirred at reflux for 2 hours more, at which time infra-redspectrospcopic analysis should indicate completion of the reaction. Thesolution is rotary evaporated to remove solvent and thionyl chloride.The PEG 600 bisacyl chloride is stirred in a hot water bath under anitrogen stream to remove traces of HCl and is taken up in 40 mL of drytoluene. Then, 10.0 mL of azidotrimethylsilane (8.7 g, 75 mmol; Aldrich155071) is added and the solution is stirred under nitrogen and slowlyheated in an oil bath to 80° C. over 45 min and then held at 80° C. for15 min. The solution is rotary evaporated from a 70° C. water bath, thenheld in the bath and stirred under a nitrogen stream for 2 hours, andfinally is stirred under high vacuum in the water bath for 1 hour toyield 14.5 g of PEG 600 diisocyanate as a brown liquid. PEG 600 bisacylchloride IR (neat): 1805 cm⁻¹ (COCl) PEG 600 diisocyanate IR (neat):2252 cm⁻¹(NCO)

¹H NMR (CDCl₃): 3.64 ppm (s, 47H, a); 3.69 (m, 4H, b); 3.75 (m, 4H, c);4.84 (s, 4H, d); 4.18 (s, 0.5H); 4.30 (t, 0.5H)

Example 1 Preparation of an Anhydrous Fibrous Sheet Comprising DextranAldehyde and Eight-Arm PEG 40K Hexadecaamine (P8-40-2)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising a fibrous polymer containing dextran aldehydeand dextran that is impregnated with eight-arm PEG 40K hexadecaamine(P8-40-2). A solution containing dextran aldehyde and dextran waselectro-blown spun into a fibrous dextran sheet, into which was addedfinely ground solid P8-40-2 PEG amine.

A mixture of 20 g of dextran aldehyde solution containing 25 wt % ofD10-48 (M_(w)=10 kDa; oxidation level=48% of glucose rings cleaved todialdehydes; prepared as described in Reagent Preparations) in water and7 g of dextran 100K (M_(w)=100 kDa; Aldrich D4876) was prepared. Themixture initially gave a fluid solution but became a gel on standing at22° C. for 30 min. The gel was stirred and warmed to 50° C. with 10 g ofwater to give a fluid solution which was stable over 3-4 hours; thissolution contained 14 wt % D10-48 and 19 wt % dextran 100K. Thissolution was spun into fibers by electro-blown spinning.

The electro-blown spinning apparatus consisted of a 0.016 inch (0.41 mm)metal tube orifice in the center of a polytetrafluoroethylene (PTFE)plate charged at 100 kV relative to a grounded target, which was arotating 8-inch (20.3 cm) diameter metal drum covered with a REEMAY®spunbonded polyester (Fiberweb Inc., London) support fabric to receivethe spun fiber which accumulated to form a sheet on the drum. Thesolution containing dextran aldehyde (D10-48) and dextran 100K was fedto the orifice via a plastic syringe pressurized with nitrogen. Theorifice was positioned pointing down toward the target drum from 24-36cm away and a concentric airflow was provided around the outside of theorifice to collimate and direct the fibers toward the metal drum. Thecurrent across the gap between the orifice and drum was typically about40-60 pA. Depending on the polymer solution viscosity, nitrogenpressures of 30-120 psig (207-827 kPa) were used to extrude the polymersolution from the spinning orifice at about 1 mL/min in droplets thatwere attenuated into fibers by the air stream and the electrostaticfield. The spinning unit was contained in a clear polycarbonate box.Relative humidity in the spinning chamber was kept at about 10-20% at25-30° C. by means of two heated nitrogen streams impinging on oppositesides of the metal drum.

The solution spun very well; the fiber plume was quite wide, indicatingthe polymer solution was well-charged. The fibrous polymer mat spun fromthis solution was about a millimeter thick, and contained 42 wt % D10-48and 58 wt % dextran 100K. The fibers had an average diameter of about700-800 nm. The aldehyde equivalent weight (CHO EW) of this fibrouspolymer was 364. A scanning electron micrograph of the dextranaldehyde/dextran fibrous polymer is shown in FIG. 1.

The fibrous polymer obtained was impregnated with a branchedpolyethylene glycol (PEG) amine and then wet with water to effectdissolution and crosslinking to form a hydrogel via condensation of thenucleophilic PEG amine groups with electrophilic dextran aldehydegroups. Finely ground 8-arm PEG 40K hexadecaamine (27 mg), prepared asdescribed in Reagent Preparations, was spread evenly on a 20-mg piece ofthe fibrous polymer, which had been stripped from its REEMAY® backing,and rubbed in. When dampened, the fibrous sheet quickly dissolved andthen crosslinked slowly over 1 min to form an elastic hydrogel.

Example 2 Preparation of an Anhydrous Fibrous Sheet Comprising DextranAldehyde and Eight-Arm PEG 10K Octaamine (P8-10-1)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising a fibrous polymer containing dextran aldehydeand dextran that is impregnated with 8-arm PEG 10K octaamine (P8-10-1).A solution containing dextran aldehyde and dextran was electro-blownspun into a fibrous dextran sheet, into which was added finely groundsolid P8-10-1 PEG amine.

A fibrous polymer containing dextran aldehyde and dextran, was preparedas described in Example 1. Finely ground 8-arm PEG 10K octaamine(P8-10-1) was prepared as described in Reagent Preparations, and 12 mgwas spread evenly on a 16-mg piece of the fibrous polymer which had beenstripped from its REEMAY® backing, and rubbed in. When dampened withdeionized water, the fibrous sheet became a soft, tacky, elastichydrogel in 5-10 sec.

Example 3 Preparation of an Anhydrous Fibrous Sheet Comprising DextranAldehyde and Eight-Arm PEG 10K Octaamine (P8-10-1)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising a fibrous polymer containing dextran aldehydeand dextran that is impregnated with 8-arm PEG 10K octaamine (P8-10-1).A solution containing dextran aldehyde and dextran was electro-blownspun into a fibrous dextran sheet, which was wetted with a solutioncontaining the P8-10-1 PEG amine in dichloromethane.

A 52-mg (3 cm×3 cm) piece of the fibrous dextran aldehyde sheet,prepared as described in Example 1, which had been stripped from itsREEMAY® backing, was placed in an aluminum weighing pan and wettedevenly dropwise with 0.37 g of a solution containing 1.00 g of P8-10-1in 5 mL (6.5 g) of dichloromethane (13 wt % P8-10-1). The damp sheet wasquickly dried under a nitrogen stream. About 50 mg of P8-10-1 wasdeposited on the fibers (CHO:NH₂=3.8). The originally soft, flexiblesheet was now stiffer, like cardstock. When it was placed in a drop ofwater, the fibrous sheet quickly wetted but maintained its shape andcrosslinked to a slightly tacky and somewhat elastic translucenthydrogel.

Example 4 Tissue Adhesion of a Fibrous Sheet Comprising Dextran Aldehydeand Eight-Arm PEG 10K Octaamine (P8-10-1)

The following Example demonstrates the adhesion of a hydrogel formed bywetting an anhydrous fibrous sheet comprising dextran aldehyde and 8-armPEG 10K octaamine (P8-10-1) to a swine uterine horn.

Clean, fresh swine uterine horn was obtained from a local grocery andwas cut into approximately 2-3-inch (5.1-7.6 cm) sections for tissueadhesion testing. The sections were stored frozen and were thawed justbefore use.

A 47-mg (2 cm×3 cm) piece of fibrous dextran aldehyde sheet, prepared asdescribed in Example 1, which had been stripped from its REEMAY®backing, was placed in an aluminum weighing pan, wetted evenly with 0.45g of a solution of 1.00 g P8-10-1 PEG amine in 5.0 mL dichloromethaneand quickly dried under a nitrogen stream. About 60 mg of the PEG aminewas deposited on the fibers (CHO:NH₂=3.2). A 1-cm×1-cm section of thefibrous sheet was laid on a 2-inch (5.1 cm) section of damp swineuterine horn and lightly misted with water to completely wet it. Afterwetting, the sheet formed an adherent, translucent hydrogel patch. Aftera period of 1 min, the uterine horn was stretched from the ends to testthe adhesion of the hydrogel patch. The thin patch stretched with theuterine horn and did not peel up. Testing by applying a force at theedges of the patch or scraping it lightly with a spatula also did notdislodge the patch, indicating that it was well-adhered. The experimentwas repeated with another piece of fibrous sheet and another piece ofswine uterine horn with the same results, i.e., adhesion was very goodand the patch did not seem particularly fragile.

The sections of swine uterine horn with the hydrogel patches on themwere soaked in a pan of water at room temperature for 35 min. Thepatches swelled but did not dislodge and were still well-adhered,although they became rather soft. Scraping with a spatula at the edgesof the patch broke off small pieces of hydrogel, but the patch did notpeel off.

Examples 5 and 6 Sealing an Incision in a Swine Uterine Horn Using aFibrous Sheet Comprising Dextran Aldehyde and Eight-Arm PEG 10KOctaamine (P8-10-1)

The following Examples demonstrate the use of fibrous sheets comprisingdextran aldehyde and 8-arm PEG 10K octaamine (P8-10-1) to seal anincision in a swine uterine horn. A fibrous dextran aldehyde sheet wasimpregnated with P8-10-1 PEG amine at two different levels and the tworesulting fibrous sheets were used to seal an incision in a swineuterine horn.

A 12-cm×18-cm sheet (1.8 g) of a fibrous dextran aldehyde sheet,prepared as described in Example 1, which had been stripped from itsREEMAY® backing was placed in a shallow aluminum pan. The sheet wasthoroughly wetted with 20 g of a solution of 10 wt % 8-arm PEG 10Koctaamine (P8-10-1) in dichloromethane (CHO:NH₂=3.3). The pan with thewetted sheet was promptly placed in a large sealed, plastic bag toprevent condensation of moisture from the air and the sheet was driedunder a stream of nitrogen from a hose placed into the bag for 10 min.The impregnated fibrous sheet was then placed under high vacuum andevacuated for 1 hour, producing a stiff, rather friable dry sheet. Thesheet was stored in a nitrogen-filled, sealed plastic bag. This fibroussheet was used in Example 5.

A second 12-cm×18-cm sheet (2.5 g) of the fibrous dextran aldehydesheet, prepared as described in Example 1, which had been stripped fromits REEMAY® backing was placed in a shallow aluminum pan lined with aPTFE sheet. The fibrous dextran aldehyde sheet was thoroughly wettedwith 20 g of a solution of 10 wt % 8-arm PEG 10K octaamine (P8-10-1) indichloromethane (CHO:NH₂=4.5) and dried under nitrogen and vacuum asdescribed above. This fibrous sheet was used in Example 6.

The two fibrous sheets were cut into 1.5-cm×3-cm (0.13-0.16 g)rectangular patches. The smoother topside of the patch (away from theoriginal REEMAY® support) was usually applied to the tissue. A 1-cmtransverse incision was made with scissors in the center of a 2-inch(5.1 cm) section of fresh swine uterine horn and the uterine horn wasconnected with a nylon tie to the nipple of a feed line from a syringepump with a pressure gauge; the other end of the uterine horn was closedwith a hemostat clamp. The syringes were filled with dyed water. Theuterine horn was dampened and a piece of anhydrous fibrous sheet waspressed firmly over the incision and then was dampened with one squirtof water from a spray mister to dissolve the fibers and form thehydrogel patch, which immediately became limp and conformed to thecontours of the tissue. After 2 min, the patched uterine horn wasimmersed in a large pan of water and water pressure was applied via thesyringe pump until the patch leaked as evidenced by a stream of dye fromthe patched area of the uterine horn. The mean leak pressures andstandard deviations are given in Table 1. In general, adhesion of thehydrogel patch to the uterine horn was excellent; about half thefailures were due to edge leaks around the highly-curved mesentery sideof the uterine horn. If no patch was placed on the incision, the leakpressure was <0.1 psig (<0.7 kPa).

TABLE 1 Leak Pressures of Sealed Incisions in Swine Uterine Horn ExampleNumber of Trials Leak Pressure, psig 5 11 0.66 ± 0.13 (4.6 ± 0.9 kPa) 624 0.77 ± 0.05 (5.3 ± 0.3 kPa)

The swine uterine horn sealing experiments described above were repeatedusing two fibrous sheets of Example 5, one applied over the other. Themean leak pressure was 1.23±0.32 psig (8.5±2.2 kPa) for three trials.

These results demonstrate that the anhydrous fibrous sheets containingdextran aldehyde and P8-10-1 PEG amine are effective in sealingincisions in swine uterine horn and suggest that the fibrous sheetswould be useful as a tissue adhesive and sealant.

Example 7 Preparation of an Anhydrous Fibrous Sheet Comprising DextranAldehyde and Four-Arm PEG K Tetraamine (P4-2-1)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising dextran aldehyde and a 4-arm PEG 2K tetraamine(P4-2-1). A solution containing dextran aldehyde and dextran waselectro-blown spun into a fibrous dextran aldehyde sheet, which wascoated with a solution containing P4-2-1.

A fibrous dextran aldehyde sheet was prepared as follows. A solution of20.0 g dextran aldehyde solution containing 25 wt % of D10-50 ((M_(w)=10kDa; oxidation level=50% of glucose rings cleaved to dialdehydes;prepared as described in Reagent Preparations) in water and 5 g ofdextran 100K (M_(w)=100 kDa; Aldrich D4876) was prepared and allowed tostand for 2 hours, at which point it gelled. With the addition of 3 g ofwater and stirring the gel at room temperature for 2 hours, a flowableviscous solution was obtained. This dextran solution contained 18 wt %D10-50 and 18 wt % dextran 100K.

The dextran solution was electro-blown spun at 100 kV according to themethod described in Example 1 to form a fibrous dextran sheet about amillimeter thick, which contained 50 wt % dextran aldehyde and 50 wt %dextran 100K (CHO EW=292). The fiber diameter was on the order of 2-3μm.

A 25-g sample of 4-arm PEG 2K tetraamine, prepared as described inReagent Preparations, was combined with 100 mL of toluene and thesolution was rotary evaporated under vacuum pump aspiration (about 3 mmHg, 0.4 kPa) from a hot water bath (80° C.) to azeotrope off water.After toluene stopped distilling off, the vacuum and heat source wereinterrupted and the flask was held in the water bath under a nitrogenstream as it slowly cooled. The yield of 4-arm PEG 2K tetraamine was25.3 g; so the PEG amine contains about 1 wt % residual toluene. Theflask of 4-arm PEG 2K tetraamine was transferred into a nitrogen-filledglove box, rebottled, and stored and used in the box to avoid moistureuptake.

The fibrous dextran aldehyde sheet was coated with P4-2-1 PEG amine asfollows. Two 4 inch×12 inch (10.2 cm×30.5 cm) sheets of the fibrousdextran sheet were rolled up in a cylindrical vacuum flask and were heldunder high vacuum (0.05 mm of mercury, 6.7 Pa) at room temperature for18 hours in an attempt to rigorously dry the fibers. The flask wastransferred to a nitrogen-filled glove box still under vacuum and thefibrous dextran aldehyde sheets were removed and transferred to sealedplastic bags in the glove box.

A 8-cm×10-cm sheet (0.71 g) of the dried fibrous dextran aldehyde sheet,which had been stripped from its REEMAY® backing, was placed in ashallow aluminum pan lined with a PTFE sheet. The fibrous dextranaldehyde sheet was thoroughly wetted with a solution of 0.3 g of dried4-arm PEG 2K tetraamine in 12 mL of dichloromethane (CHO:NH₂=4.0). Thewet fibrous sheet was dried under a stream of nitrogen for 15 min andthe pan was then placed in a vacuum chamber and evacuated for 40 min.This produced a soft, dry-appearing fibrous sheet resembling theoriginal fibrous dextran sheet. The fibrous sheet was stored in a sealedplastic bag under nitrogen in the glove box until use.

Examples 8 and 9 Sealing an Incision in a Swine Uterine Horn Using aFibrous Sheet Comprising Dextran Aldehyde and Four-Arm PEG Tetraamine(P4-2-1)

The following Examples demonstrate the use of an anhydrous fibrous sheetcomprising dextran aldehyde and 4-arm PEG 2K tetraamine (P4-2-1) to sealan incision in a swine uterine horn.

The anhydrous fibrous sheet described in Example 7 was cut into2-cm×3-cm rectangular patches, each weighing about 0.06-0.09 g. Thesmoother topside of the patch away from the original REEMAY® backing wasusually applied to the tissue because this side may be somewhat morealdehyde-rich as the PEG amine may concentrate at the bottom duringimpregnation and evaporation. It is believed that placing thealdehyde-rich side of the fibrous sheet in contact with the tissue mayincrease adhesion due to the interaction of the aldehyde groups withfree amine groups on the tissue.

This anhydrous fibrous sheet was used to seal a swine uterine horn, asdescribed in Examples 6 and 7. Fibrous sheets were lightly pressed ontothe damp swine uterine horn over a 1-cm incision and lightly tamped downaround the perimeter to help establish a bond to the tissue. Then, thesheet was misted with a plant mister to wet it completely (Example 8).When a second sheet was used (Example 9), it was immediately appliedover the first patch in the same manner. The sheet was allowed tocrosslink for a minute before immersing in water and pressure testing.The results of the pressure testing are summarized in Table 2.

TABLE 2 Leak Pressures of Sealed Incisions in Swine Uterine Horn Numberof Fibrous Leak Pressure, Example Sheets Number of Trials psig 8 1 20.42 ± 0.20 (2.9 ± 1.4 kPa) 9 2 6 0.80 ± 0.27 (5.5 ± 1.9 kPa)

The results demonstrate that the anhydrous fibrous sheets containingdextran aldehyde and P4-2-1 PEG amine were effective in sealingincisions in swine uterine horn and suggest that the fibrous sheetswould be useful as a tissue adhesive and sealant.

Example 10 Preparation of an Anhydrous Fibrous Sheet ComprisingPoly(Vinyl Alcohol-Co-Vinyl Amine) and Four-Arm PEG 2KTetra(Thiomethylaldehyde)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising poly(vinyl alcohol-co-vinyl amine) and 4-armPEG 2K tetra(thiomethylaldehyde). A solution containing poly(vinylalcohol-co-vinyl amine) was electro-blown spun into a fibrous polymersheet, which was coated with solution containing 4-arm PEG 2Ktetra(thiomethylaldehyde).

A solution containing 20 wt % of poly(vinyl alcohol-co-vinyl amine),prepared as described in Reagent Preparations Method A, waselectro-blown spun at 100 kV under conditions similar to those given inExample 1 to give a fibrous polymer sheet about a millimeter thickhaving a fiber diameter of about 1-3 μm. A scanning electron micrographof the poly(vinyl alcohol-co-vinyl amine) fibrous polymer is shown inFIG. 2. This fibrous poly(vinyl alcohol-co-vinyl amine) polymer sheetwas stored in a nitrogen-filled glove box and kept protected fromatmospheric carbon dioxide. The sheet was very hydrophilic and wouldcling tenaciously to one's hands if they were even slightly damp.

A 10-cm×12-cm sheet (0.75 g) of the poly(vinyl alcohol-co-vinyl amine)fibrous polymer, which had been stripped from its REEMAY® backing, wasplaced in a shallow aluminum pan lined with a PTFE sheet. The pan wasplaced in a nitrogen-filled glove box, and the fibrous sheet wasthoroughly wetted with a solution of 0.30 g 4-arm PEG 2Ktetra(thiomethylaldehyde), prepared as described in ReagentPreparations, in 10 mL of dichloromethane (CHO:NH₂=0.31). The wettedsheet was dried under a stream of nitrogen for 15 min and the pan wasthen placed in a vacuum chamber and evacuated for 20 min, producing asoft, dry-appearing sheet resembling the original fibrous poly(vinylalcohol-co-vinyl amine) polymer sheet. The fibrous sheet comprisingpoly(vinyl alcohol-co-vinyl amine) and the four-arm PEG 2Ktetra(thiomethylaldehyde) was stored in a sealed plastic bag undernitrogen in the glove box until use.

Example 11 Sealing an Incision in a Swine Uterine Horn Using a FibrousSheet Comprising Poly(Vinyl Alcohol-Co-Vinyl Amine) and Four-Arm PEG 2KTetra(Thiomethylaldehyde)

The following Example demonstrates the use of an anhydrous fibrous sheetcomprising poly(vinyl alcohol-co-vinyl amine) and 4-arm PEG 2Ktetra(thiomethylaldehyde) to seal an incision in a swine uterine horn.

The fibrous sheet comprising poly(vinyl alcohol-co-vinyl amine) and4-arm PEG 2K tetra(thiomethylaldehyde), prepared as described in Example10, was cut into 1.5-cm×2-cm rectangular patches. The weights of thepatches were about 50-60 mg. The smoother topside of the patch wasalways applied to the tissue for reasons described in Examples 8 and 9.This fibrous sheet was used to seal an incision in a swine uterine horn,as described in Examples 5 and 6. A single patch was lightly pressedonto the damp swine uterine horn over a 1-cm incision and lightly tampeddown around the perimeter to help establish a bond to tissue and thenallowed to cure for 1 min before pressure testing. The patches weretypically not wetted further with a mister after application.

The mean leak pressure for ten trials in this test was 1.79±1.30 psig(12.3±9.0 kPa). This result demonstrates that the anhydrous fibroussheet comprising poly(vinyl alcohol-co-vinyl amine) and 4-arm PEG 2Ktetra(thiomethylaldehyde) is effective in sealing incisions in swineuterine horn and suggests that the fibrous sheet would be useful as atissue adhesive and sealant.

Example 12 Preparation of an Anhydrous Fibrous Sheet ComprisingPoly(Vinyl Alcohol-Co-Vinyl Amine) and PEG 600 Bisthiomethylaldehyde)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising poly(vinyl alcohol-co-vinyl amine) and PEG 600bis(thiomethylaldehyde). A solution containing poly(vinylalcohol-co-vinyl amine) was electro-blown spun into a fibrous polymersheet, which was coated with a solution containing PEG 600bis(thiomethylaldehyde).

An 8-cm×10-cm sheet (0.48 g) of the poly(vinyl alcohol-co-vinyl amine)fibrous polymer sheet, described in Example 10, which had been strippedfrom its REEMAY® backing, was placed in a shallow aluminum pan linedwith a PTFE sheet. The pan was placed in a nitrogen-filled glove box,and the fibrous sheet was thoroughly wetted with a solution of 0.18 gPEG 600 bis(thiomethylaldehyde), prepared as described in ReagentPreparations, in 10 mL of dichloromethane (CHO:NH₂=0.49). The wettedsheet was dried under a stream of nitrogen for 15 min and the pan wasthen placed in a vacuum chamber and evacuated for 10 min, producing asoft, dry-appearing sheet resembling the original sheet of poly(vinylalcohol-co-vinyl amine) fibrous polymer. The sheet was stored in asealed plastic bag under nitrogen in the glove box until use.

Example 13 Preparation of an Anhydrous Fibrous Sheet ComprisingPoly(Vinyl Alcohol-Co-Vinyl Amine) and PEG 600 Bis(Thiomethylaldehyde)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising poly(vinyl alcohol-co-vinyl amine) and PEG 600bis(thiomethylaldehyde). A solution containing poly(vinylalcohol-co-vinyl amine) was electro-blown spun into a fibrous polymersheet, which was coated with a solution containing PEG 600bis(thiomethylaldehyde).

A 7-cm×10-cm sheet (0.43 g) of the poly(vinyl alcohol-co-vinyl amine)fibrous polymer sheet, described in Example 10, which had been strippedfrom its REEMAY® backing, was placed in a shallow aluminum pan linedwith a PTFE sheet. The pan was placed in a nitrogen-filled glove box,and the fibrous sheet was thoroughly wetted with a solution of 0.25 gPEG 600 bis(thiomethylaldehyde), prepared as described in ReagentPreparations, in 10 mL of dichloromethane (CHO:NH₂=0.76). The wettedsheet was dried under a stream of nitrogen for 15 min and the pan wasthen placed in a vacuum chamber and evacuated for 10 min, producing asoft, dry-appearing sheet resembling the original sheet of poly(vinylalcohol-co-vinyl amine) fibrous polymer. The sheet was stored in asealed plastic bag under nitrogen in the glove box until use.

Examples 14 and 15 Sealing an Incision in a Swine Uterine Horn UsingFibrous Sheets Comprising Poly(Vinyl Alcohol-Co-Vinyl Amine) and and PEG600 Bis(Thiomethylaldehyde)

The following Examples demonstrate the use of anhydrous fibrous sheetscomprising poly(vinyl alcohol-co-vinyl amine) and PEG 600bis(thiomethylaldehyde) to seal an incision in a swine uterine horn.

The anhydrous fibrous sheets described in Examples 12 and 13 weresubjected to the swine uterine horn burst test described in Examples 5and 6. The fibrous sheets were cut into 1.5-cm×2-cm rectangular pieces.The weights of most of the rectangles were about 60 mg, but there werealso some thin patches of about 20-30 mg. The smoother topside of thepatch away from the original REEMAY® support was always applied to thetissue. A single patch was lightly pressed onto the damp swine uterinehorn over the 1-cm incision and lightly tamped down around the perimeterto help establish a bond to the tissue and allowed to cure for 60 secbefore pressure testing. The patches were not wetted further with amister after application. In a few experiments, the patch was pressedonto the damp tissue and then the uterine horn section was immediatelyimmersed in water for 60 sec while the patch cured. Burst pressures wereas high in those cases as when the patch was cured in air. The mean leakpressures and standard deviations are given in Table 3.

TABLE 3 Leak Pressures of Sealed Incisions in Swine Uterine Horn LeakPressure, Example Fibrous Sheet Number of Trials psig 14 from Example 1210 2.17 ± 1.17 (15.0 ± 8.1 kPa)  15 from Example 13 8 1.39 ± 0.91 (9.58± 6.27 kPa)

The results demonstrate that the anhydrous fibrous sheets containingpoly(vinyl alcohol-co-vinyl amine) and PEG 600 bis(thiomethylaldehyde)were effective in sealing incisions in swine uterine horn and suggestthat the fibrous sheets would be useful as a tissue adhesive andsealant. Adhesion was good in all cases and better than cohesion. Atrace of hydrogel adhesive remained on the tissue when a patch waspulled off. The lower PEG 600 bis(thiomethylaldehyde) loading appearedto give higher burst pressures (Example 14) than higher loading (Example15). Leaks were typically at the edges, due to failure of the patch toconform to the highly-curved tissue surface. It is important for thepatch to be in intimate contact with the tissue while it is initiallybeing wetted for good adhesion at the edges. The thinner patches, whilelacking the cohesive strength of the thicker patches, conformed andadhered very well to curved tissue surfaces.

Example 16 Preparation of an Anhydrous Fibrous Sheet Comprising DextranAldehyde and Dextran Acetoacetate

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising dextran aldehyde and dextran acetoacetate. Thefibrous sheet was formed by electro-blown spinning a solution containinga mixture of both components.

A mixture of 15 g dextran aldehyde solution containing 25 wt % of D10-48(prepared as described in Reagent Preparations) in water and 5 g ofdextran acetoacetate, prepared as described in Reagent Preparations,containing 3 drops of acetic acid to forestall condensation wasprepared. The mixture initially gave a viscous solution but soon becamea gel. Stirring and heating with 5 g of water gave a solution whichbegan to gel again on cooling (omitting the acetic acid resulted in acrosslinked gel which did not dissolve in excess water and did notliquefy on warming). Rewarming the mixture gave a fluid, spinnablesolution which contained 15 wt % D10-48 and 20 wt % dextranacetoacetate. This solution was electro-blown spun into fibers, asdescribed in Example 1. The fiber plume was narrower than with thesolution of Example 1. Although the polymer apparently was not taking onas much charge, it still spun well. The average fiber diameter was about1600 nm (1.6 μm). The fibrous sheet contained 33 wt % D10-48 and 67 wt %dextran acetoacetate, and was a few mm thick but was very easilycompacted with handling, e.g., upon applying pressure, the sheetflattened to a thickness of about 0.01 inches (0.25 mm). The fibroussheet had reasonable strength and could be handled without tearing,although it could be torn without difficulty. The sheet was veryhydrophilic and would cling tenaciously to one's hands if they were evenslightly damp.

The fibrous sheet comprising dextran aldehyde and dextran acetoacetatewas treated with aqueous base to effect dissolution and crosslinking toa hydrogel via condensation of the nucleophilic conjugate base of theacidic acetoacetate methylenes with electrophilic dextran aldehydegroups. Specifically, upon spraying a piece of the fibrous sheet, whichhad been stripped from its REEMAY® backing, with an aqueous solutioncontaining 10 wt % sodium carbonate, the dampened fibrous sheet becametranslucent but retained its shape as a result of crosslinking to form afriable, unswollen hydrogel.

Spraying the fibrous sheet as described above, but using a dilute sodiumcarbonate solution (i.e., 0.2 wt %) for wetting resulted in theformation of a clear, crosslinked hydrogel which was slightly swollen.The fibrous sheet retained its shape and could be handled somewhat butwas rather weak.

Spraying the fibrous sheet as described above, but using water oraqueous phosphate buffer (pH 7.4) for wetting did not result in theformation of a crosslinked hydrogel because a stronger base is requiredto form the nucleophilic conjugate base of acetoacetate to react withthe electrophilic dextran aldehyde groups.

Additionally, finely ground sodium bicarbonate (20 mg) was spread evenlyon a 23-mg piece of the fibrous sheet containing dextran aldehyde anddextran acetoacetate, which had been stripped from its REEMAY® backing,and rubbed in. When dampened with water, the fibrous sheet becametranslucent, but maintained its shape as a stiff, weak hydrogel.

Example 17 Preparation of an Anhydrous Fibrous Sheet Comprising FibrousDextran Aldehyde and Fibrous Poly(Vinyl Alcohol-Co-Vinyl Amine)

The following Example demonstrates the preparation of an anhydrousbilayer fibrous sheet comprising a layer of nucleophilic poly(vinylalcohol-co-vinyl amine) fiber and a layer of electrophilic dextranaldehyde/dextran 100K fiber.

A mixture of 10 g of poly(vinyl alcohol-co-vinyl amine) polymer,prepared as described in Reagent Preparations, Method B, and 45 g ofdeionized water was stirred at 70° C. in a water bath for 2 hours togive a viscous solution containing 18 wt % of the polymer. This solutionwas used to spin the poly(vinyl alcohol-co-vinyl amine) polymer into afibrous sheet.

A mixture of 30 g of a dextran aldehyde solution (D10-50, 25 wt %)(starting dextran M_(w)=10 kDa; 50 mol % of the glucose rings wereoxidized to dialdehydes) and 9 g of dextran100K (M_(w)=100 kDa; AldrichD4876) was stirred at room temperature for 10 min and then 6 g water wasadded and the solution was stirred 5 min more. The solution contained 17wt % D10-50 and 20 wt % dextran100K; 37 wt % total solids.

The solid fiber spun from this solution had the composition D10-50dextran aldehyde 46 wt %/dextran 100 kDa 54 wt % (CHO EW=340).

In the electro-blown spinning apparatus, described in Example 1, thetotal takeup drum area covered by the REEMAY® backing was about 1900cm². The aim was to lay down a layer of each polymer fiber about 1mg/cm² thick, which is equivalent to about 2 g total of each polymerfiber over this area. For an 18 wt % solution of poly(vinylalcohol-co-vinyl amine) with a density of about 1.2, around 10 mL ofsolution had to be spun to give a 1 mg/cm² fibrous sheet. For a 37 wt %solution of dextran aldehyde/dextran 100K with similar density, about 5mL of solution was needed to be spun to give a 1 mg/cm² fibrous sheet.The takeup drum was moved to the lower position (36 cm away fromorifice) to improve the distribution of the fiber over the REEMAY®support. A layer of fiber from 10 mL of 18 wt % poly(vinylalcohol-co-vinyl amine) solution was electro-blown spun onto the drumover 25 min at 120 psig (827 kPa) followed by a layer of fiberelectro-blown spun from 5 mL of 37 wt % dextran aldehyde/dextran 100Ksolution over about 4 min at 40 psig (276 kPa). This bilayer fibroussheet had a CHO:NH₂ ratio=1.15. The fibrous sheet was stored in asealed, plastic bag in a nitrogen-filled glove box until use.

Examples 18 and 19 Sealing an Incision in a Swine Uterine Horn UsingFibrous Sheets Comprising Poly(Vinyl Alcohol-Co-Vinyl Amine) and DextranAldehyde

The following Examples demonstrate the use of anhydrous fibrous sheetscomprising alternating layers of fibrous poly(vinyl alcohol-co-vinylamine) and fibrous dextran aldehyde to seal an incision in a swineuterine horn.

A 2.5-cm×37-cm (93 cm²) section from the center of the bilayer fibroussheet comprising poly(vinyl alcohol-co-vinyl amine) and dextranaldehyde/dextran 100K, described in Example 17, was stripped from theREEMAY® backing. The fibrous sheet weighed 200 mg, and although thesheet was not quite uniform in thickness, this is equivalent to about2.2 mg/cm². This strip of fibrous sheet was cut in the middle into twostrips the same width and half the original length, and the two stripswere individually wound around a 1.8-cm diameter rod. The wound-up rollswere each slit in the transverse direction with a razor blade andflattened out into 2.5-cm×6-cm layered sheets that were comprised ofthree or four layers of alternating poly(vinyl alcohol-co-vinyl amine)and dextran aldehyde/dextran 100K. Each multilayered sheet was cut intothree 2.5-cm×2-cm rectangular pieces weighing about 30 mg. In Example18, a single piece of the multilayered fibrous sheet was used to seal anincision in a swine uterine horn as described in Examples 5 and 6.

Another 2-cm×37-cm section from the center of the bilayer fibrous sheetcomprising poly(vinyl alcohol-co-vinyl amine) and dextranaldehyde/dextran 100K, described in Example 17, was stripped from theREEMAY® backing and cut into 1.5-cm×2-cm patches; each of these patchesweighed only about 6 mg. In Example 19, four or five of thesesingle-thickness bilayer patches were applied on top of one another overan incision in a swine uterine horn to build up a multilayer patch whichwas subjected to the swine uterine horn burst test described in Examples5 and 6.

In the burst testing, the fibrous patch was firmly pressed, amine sidedown (i.e., with the poly(vinyl alcohol-co-vinyl amine) fiber faceexposed to the tissue surface), onto the damp swine uterine horn overthe 1-cm incision and the edges were tamped down with a dry spatula toeffect a seal. When the multilayer patch of Example 18 was used, thepatch on the uterine horn was misted with water to wet it through andthen it was allowed to cure for 60 sec before immersing the swineuterine horn in water and pressure testing. When the single-thickness,bilayer fibrous patch of Example 19 was used to build up a multilayer,the first patch was pressed onto the damp tissue amine side down. Whenthe first patch had absorbed enough water to wet through, the next patchwas applied, also amine side down, with no or minimal additionaldampening. In this way a multilayer structure of 4 or 5 patches wasbuilt up, misting with water only after every other patch application.Care was taken to interface opposite fiber layers when building up amultilayer patch to optimize crosslinking; i.e., dextran aldehyde fiberwas applied facing poly(vinyl alcohol-co-vinyl amine) fiber. The patcheswere allowed to cure 60 sec before immersing in water and pressuretesting. The results of the pressure testing are summarized in Table 4.

TABLE 4 Leak Pressures of Sealed Incisions in Swine Uterine Horn Numberof Fibrous Leak Pressure, Example Patches Number of Trials psig 18 1multilayer 5 0.38 ± 0.15 (2.6 ± 1.0 kPa) 19 4-5 single bilayer 4 0.52 ±0.13 (3.6 ± 0.9 kPa)

The results demonstrate that the anhydrous fibrous sheets comprisingalternating layers of fibrous poly(vinyl alcohol-co-vinyl amine) andfibrous dextran aldehyde were effective in sealing incisions in swineuterine horn and suggest that the fibrous sheets would be useful as atissue adhesive and sealant.

Example 20 Preparation of an Anhydrous Fibrous Sheet ComprisingPoly(Vinyl Alcohol-Co-Vinyl Amine) and Linear PEG 600 Diisocyanate

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising poly(vinyl alcohol-co-vinyl amine) and PEG 600diisocyanate. A solution containing poly(vinyl alcohol-co-vinyl amine)was electro-blown spun into a fibrous polymer sheet, which was coatedwith a solution containing PEG 600 diisocyanate.

A poly(vinyl alcohol-co-vinyl amine) polymer was prepared according toMethod B in the Reagent Preparation section above, except no chaintransfer agent was employed. This provided a higher molecular weightpoly(vinyl alcohol-co-vinyl amine) (M_(w)=1000K) with about 10 mol %amine. A 12 wt % solution of this poly(vinyl alcohol-co-vinyl amine)solution was electro-blown spun, using the apparatus described inExample 1, at 100 kV using a solution feed rate of 0.5 mL/min to give afibrous polymer sheet having a fiber diameter of about 0.5-1 μm. Thedistance from the orfice to the drum was about 40 cm in theelectro-blown spinning process. The resulting poly(vinylalcohol-co-vinyl amine) fibrous polymer sheet was stored in anitrogen-filled glove box and kept protected from atmospheric carbondioxide.

A 7-cm×10-cm sheet (0.22 g, the sheet was thin compared to other fibroussheets tested in the previous Examples) of the poly(vinylalcohol-co-vinyl amine) fibrous polymer sheet which had been strippedfrom its Reemay® backing was placed in a shallow aluminum pan that hadbeen lined with a PTFE sheet. The pan was placed in a nitrogen-filledglove box, and the sheet was thoroughly wetted with a solution of 0.10 gPEG 600 diisocyanate, prepared as described in Reagent Preparation, in10 mL of dichloromethane (NCO:NH2=0.67). The wet sheet was dried under astream of nitrogen for 15 min and the pan was then placed in a vacuumchamber and evacuated for 10 min. This produced a soft, dry-appearingsheet resembling the original fibrous polymer sheet. The sheet wasstored in a sealed plastic bag under nitrogen in the glove box untiluse.

Example 21 Sealing an Incision in a Swine Uterine Horn with an AnhydrousFibrous Sheet Comprising Poly(Vinyl Alcohol-Co-Vinyl Amine) and PEG 600Diisocyanate

The following Example demonstrates the use of an anhydrous fibrous sheetcomprising poly(vinyl alcohol-co-vinyl amine) and PEG 600 diisocyanateto seal an incision in a swine uterine horn.

The anhydrous fibrous sheet comprising poly(vinyl alcohol-co-vinylamine) and PEG 600 diisocyanate, described in Example 20, was subjectedto the swine uterine horn burst test described in Examples 5 and 6. Thesheets were cut into 1.5-cm×2-cm rectangular pieces. The weight of mostof the rectangles was about 15 mg. A single patch was lightly pressedonto the damp swine uterine horn over the 1-cm incision and lightlytamped down around the perimeter to help establish a bond to tissue,misted once and allowed to cure 60 sec before pressure testing. Adhesionwas excellent in all cases and burst pressures were high despite thethin patches, specifically, the mean leak pressure for two trials was3.70±0.28 psig (25.5±1.93 kPa).

Example 22 Preparation of an Anhydrous Fibrous Sheet Comprising DextranAldehyde of Two Different Molecular Weights and Eight-Arm PEG 10KOctaamine (P8-10-1)

The following Example demonstrates the preparation of an anhydrousfibrous sheet comprising a fibrous polymer containing dextran aldehydeof two different molecular weights that is impregnated with 8-arm PEG10K octaamine (P8-10-1) by wetting with a solution containing theP8-10-1 PEG amine in dichloromethane.

A fibrous polymer sheet containing dextran aldehyde of two differentmolecular weights was prepared as follows. A mixture of 20 g of dextranaldehyde solution containing 25 wt % of D10-50 (prepared as described inReagent Preparations) in water and 3 g of solid dextran aldehyde D100-6(prepared as described in Reagent Preparations) was prepared by stirringthe two components at 45° C. for an hour. The resulting clear solutionwas then allowed to stand at room temperature for 30 min beforespinning. This solution was electro-blown spun into fibers, as describedin Example 1. Upon spinning at 10-20 psig feed pressure and 4 psig jetpressure, the solution gave fine, short fibers (<1 cm) which laid downto give a fine felt. The average fiber diameter was 350-700 nm. Thefibrous sheet contained 63 wt % D10-50 and 37 wt % dextran aldehydeD100-6.

A 331-mg piece of the fibrous dextran aldehyde polymer sheet, preparedas described above, which had been stripped from its REEMAY® backing,was placed in an aluminum weighing pan and wetted evenly dropwise with asolution of 0.28 g of P8-10-1 in 3 mL of dichloromethane. The damp sheetwas dried under a nitrogen stream to give a composition withCHO:NH₂=7.0.

Example 23 Tissue Adhesion of a Fibrous Sheet Comprising DextranAldehyde of Two Different Molecular Weights and 8-Arm PEG 10K Octaamineon Swine Uterine Horn

A 1-cm×2-cm section of the fibrous sheet described in Example 22 waslaid on a 2-inch (5 cm) section of damp swine uterine horn and lightlymisted with water to completely wet it. After wetting, the sheet formedan adherent, translucent hydrogel patch. Testing by applying a force atthe edges of the patch or scraping it lightly with a spatula also didnot dislodge the patch, indicating that it was well-adhered. Tissueadhesion in the present case appeared superior to the correspondingcomposition of Example 4 in which the high molecular weight dextrancomponent was unfunctionalized. This improvement may be due to the factthat the high molecular weight dextran component in the fibrous sheet ofExample 22 is functionalized with a low level of aldehyde groups and isthus able to participate in the crosslinked structure of the hydrogel.

What is claimed is:
 1. A method for applying a coating to an anatomicalsite on tissue of a living organism comprising the steps of: a) applyingto the site a first component of fibrous polymer containingelectrophilic or nucleophilic groups; b) applying to the site an aqueoussolution or dispersion comprising a second component capable ofcrosslinking the first component, wherein the second component containselectrophilic groups if the first component contains nucleophilic groupsor contains nucleophilic groups if the first component containselectrophilic groups; and c) allowing the first and the second componentto crosslink on the site to form a hydrogel that is adhesive to thetissue.
 2. The method according to claim 1, wherein the electrophilicgroups of the first component are selected from the group consisting ofaldehyde, acetoacetate, and succinimidyl ester.
 3. The method accordingto claim 1, wherein the electrophilic groups of the second component areselected from the group consisting of aldehyde, acetoacetate,succinimidyl ester, and isocyanate.
 4. The method according to claim 1,wherein the nucleophilic groups of the first component are selected fromthe group consisting of primary amine, secondary amine,carboxyhydrazide, acetoacetate, and thiol.
 5. The method according toclaim 1, wherein the nucleophilic groups of the second component areselected from the group consisting of primary amine, secondary amine,carboxyhydrazide, acetoacetate, and thiol.
 6. The method according toclaim 1, wherein the fibrous polymer comprises at least onewater-dispersible polymer having electrophilic groups, wherein thewater-dispersible polymer is selected from the group consisting ofoxidized polysaccharides having aldehyde groups, poly(vinyl alcohol) orpoly(vinyl alcohol) copolymers derivatized with acetoacetate groups, andpolysaccharides derivatized with acetoacetate groups.
 7. The methodaccording to claim 1, wherein the second component comprises at leastone water-dispersible polymer having electrophilic groups, wherein thewater-dispersible polymer is selected from the group consisting ofoxidized polysaccharides having aldehyde groups, poly(vinyl alcohol) orpoly(vinyl alcohol) copolymers derivatized with acetoacetate groups,polysaccharides derivatized with acetoacetate groups, linear or branchedpolyethers derivatized with acetoacetate groups, linear or branchedpolyethers derivatized with aldehyde groups, linear or branchedpolyethers derivatized with N-hydroxysuccinimidyl ester groups, andlinear or branched polyethers derivatized with isocyanate groups.
 8. Themethod according to claim 1, wherein the fibrous polymer comprises atleast one water-dispersible polymer having nucleophilic groups, whereinthe water-dispersible polymer is selected from the group consisting ofpoly(vinyl alcohol) or poly(vinyl alcohol) copolymers having primaryamine groups, secondary amine groups, or acetoacetate groups; andpolysaccharides having primary amine groups, secondary amine groups, oracetoacetate groups.
 9. The method according to claim 1, wherein thesecond component comprises at least one water-dispersible polymer havingnucleophilic groups, wherein the water-dispersible polymer is selectedfrom the group consisting of linear or branched polyethers derivatizedwith primary amine groups or secondary amine groups; poly(vinyl alcohol)or poly(vinyl alcohol) copolymers having primary amine groups, secondaryamine groups or acetoacetate groups; polysaccharides having primaryamine groups, secondary amine groups, or acetoacetate groups; linear orbranched polyethers derivatized with thiol groups; and linear orbranched polyethers derivatized with carboxyhydrazide groups.
 10. Themethod according to claim 1, wherein the fibrous polymer comprises atleast one oxidized polysaccharide having aldehyde groups and the secondcomponent comprises at least one water-dispersible multi-arm polyetheramine.
 11. The method according to claim 10, wherein the at least oneoxidized polysaccharide is oxidized dextran and the at least onewater-dispersible multi-arm polyether amine is a multi-arm polyethyleneglycol amine.
 12. The method according to claim 1, wherein the fibrouspolymer comprises a poly(vinyl alcohol) or poly(vinyl alcohol) copolymerhaving primary amine groups or secondary amine groups and the secondcomponent comprises a linear or branched polyether derivatized withisocyanate groups.
 13. The method according to claim 1, wherein theaqueous solution or dispersion contains from about 5% to about 70% byweight of the second component relative to the total weight of theaqueous solution or dispersion.